IS 802 Part-1 (2) :1992
IS 802 Part-1 (2) :1992
IS 802 Part-1 (2) :1992
( Part
l/Set
2 ) : 1992
( Reaffirmed 2003 )
( Third Revision )
First Reprint MAY 1995
UDC
62 I *315.668.2
@ BIS 1992
BUREAU
MANAK
OF
BHAVAN,
INDIAN
STANDARDS
ZAFAR MARG
December
1992
Price Group 6
Structural
Engineering
Sectional
Committee,
CED
FOREWORD This Indian Standard ( Third Revision ) was adopted by the Bureau of Indian Standards, the draft finalized by the Structural Engineering Sectional Committee had been approved Civil Engineering Division Council. after by the
This standard has been prepared with a view to establish uniform practices for design, fabrication, testing and inspection of overhead transmission line towers. Part I of the standard covers requirements in regard to material, types of towers, loading and permissible stresses apart from Provisions for fabrication, galvanizing, inspection and packing other relevant design provisions. have been covered in Part 2 whereas provisions for testing of these towers have been covered in Part 3 of the standard. This standard ( Part 1 ) was first published in 1967 and subsequently revised in 1973 and 1977. In this revision, the code has been split in two sections namely Section 1 Materials and loads, and Other major modifications effected in this revision ( Section 2 ) Section 2 Permissible stresses. are as under: a) Permissible stresses in structural members have been given in terms of the yield strength of the material. With the inclusion of bolts of property class 5.6 of IS 12427 : 1988, permissible stresses for these bolts have also been included. for width/thickness ratio of the b) Critical stress in compression Fcr has been modified for calculating the allowable unit compressive angles exceeding the limiting value stresses. c) Effective slenderness ratios ( KL/r ) for redundant members have been included and provisions further elaborated. d) Examples for the determination of slenderness ratios have been and x bracings with and without secondary members. extended to include K
Designs provisions or other items not covered in this standard shall generally be in accordance with IS 800 : 1984 Code of practice for general construction in steel ( second revision ). While preparing this standard, practices prevailing in the country in this field have been kept in view. Assistance has also been derived from the &Guide for design of steel transmission line Society of Civil Engineers towers ( second edition ) - ASCE Manual No. 52, issued by American ( ASCE ) hew York, 1988. For the purpose of deciding whether a particular requirement of this Code is complied with, the final value, observed or calculated, expressing the result of a test, shall be rounded off in accordance with IS 2 : 1960 Rules for rounding off numerical values ( revised ). The number of significant places retained in the rounded off value should be the same as that of the specified value in this standard.
Indian Standard USE OF STRUCTURAL STEEL IN OVERHEAD TRANSMISSION LINE TOWERS - CODE OF PRACTICE
PART 1 MATERIAL, Section ( 1 SCOPE 1.1 This standard ( Part l/Set 2 ) stipulates the permissible stresses and other design parameters to be adopted in the design of self-supporting steel lattice towers for overhead transmission lines. 1.1.1 Materials, type broken wire conditions of this standard. of towers, loading and are covered in Section 1 LOADS 2 AND PERMISSIBLE Stresses STRESSES Permissible
Third Revision )
exceed the following percentage strength of the conductor: Initial unloaded tension Final unloaded tension of the ultimate
35 percent 25 percent
provided that the ultimate tension under everyday temperature and full wind or minimum temperature and two-thirds wind pressure does not exceed 70 percent of the ultimate tensile strength of the cable. 5 PERMISSIBLE 5.1 Axial Stresses STRESSES in Tension
1.1.2 Provisions on fabrication and testing of transmission line towers have been covered in Part 2 and Part 3 respectively of the standard.
NOTE - While formulating the provisions of this standard it has been assumed that the structural connections are through bolts.
1.2 This standard does not cover guyed towers. These will be covered in a separate standard. 2 REFERENCES The Iudian Standards listed in Annex necessary adjuncts to this standard. 3 STATUTORY REQUIREMENTS A are
The estimated tensile stresses on the net effective sectional areas ( see 9 ) in various members, shall not exceed minimum guaranteed yield stress of the material. However in case the angle section is connected by one leg only, the estimated tensile stress on the net effective sectional area shall not exceed FY ,where F, is the minimum guaranteed yield stress of the material. 5.2 Axial Stresses in Compression stresses in the values
3.1 Statutory requirement as laid down in the Indian Electricity Rules. 1956 or by any other statutory code applicable to such structures shall be followed. 3.2 Compliance with this code does not relieve any one from theresponsibilityof observing local and state byelaws, fire and safety laws and other civil aviation requirements applicable to such structures. 4 CONDUClOR TENSION
5.2.1 The estimated compressive various members shall not exceed given by the formulae in 5.2.2.
5.2.2 The allowable unit stress F,, in MPa on the gross cross sectional area of the axially loaded compression members shall be: a) F*=[l-f(+$-)a]xF, when KLIr < CC and, b,
1
4.1 The conductor tension at everyday temperature and without external load should not
Fa =
9 x E ( KL/r )
Table I
Bolts of
Stress
Remarks
of steel
L = unbraced length of the compression member ( see 6.1.1 ) in cm, and radius of gyration in cm. r z appropriate formulae given in 5.2.2 are applicable provided the largest width thickness ratio b/t is not more than the limiting value given by: ( b/t )lim =z 210/i/ Fy where b= t = distance extreme thickness from edge of fillet fibre in mm, and of flange in mm. to the
area of bolts
5.2.2.1 The
For gross area of bolts ( see 10.4). For bolts in double shear the area to be assumed shall be twice the area defined For the bolt area in bearing
( see 10.5 )
Bearing
436
620
194 RATIOS
2.50
5.X2.2 Where the width thickness ratio exceeds the limits given in 5.2.2.1, the formulae given in 5.2.2 shall be used substituting for &. the value F,, given by:
6.1 The slenderness ratios of eompression redundant members shall be determined follo\vs: Type of Members a) Compression Members
and as
Value of KL]r
a) Fe, =
anu,
1.677 _
b) Fe, =
65 550 ( b,t )_
i) Leg sections or joint members bolted in both faces at connections for 0 c L/r Q 120 ii) Members with concentric loading at both ends of the unsupported pane1 for 0 < L/r c 120 iii) Member with concentric loading at one end and normal framing eccentricity at the other end of the unsupported panel for 0 c Ljr c 1.20 with normal iv) Member framing eccentricities at both ends of the unpanel for supported 0 c L/r c 120 30 t-0.75
Llr
when
Llr
NOTE - The,maximum permissible value of b/lr for any type of steel shall not exceed 25.
5.3 The redundant members shall be checked individually for 2.5 percent of axial load carried by the member to which it supports.
5.4 Stresses
in Bolts
L/r
Ultimate stresses in bolts conforming to property class 4.6 of IS 6639 : 1972 and to property class 5.6 of IS 12427 : 1988 shall not exceed the value given in Table I. For bolts conforming stresses and other to IS 3757 : 1985, permissible provisions governing the use of high strength bolts reference shall be made to IS 4000 : 1992. 5.4.1 Where the material of bolt and the structural member are of different grades, the bearing strength of the joint shall be governed by the lower of the two.
60 + 0.50
L/t
VI Member
unrestrained against rotation at both ends of the unsupported pane1 for 120 c Lfr S 200
L/r
IS 802 ( Part l/Set vi) Member partially restrained against rotation at one end of the unsupported panel fnr 120 < L/r < 225 vii) Member partially rcstrained against rotation at both ends of the unsupported panel for 120 < L/r < 250 b) Redundant Members i) For 0 < L/r c 250 28.6 + O-762 L[r 7 MINIMUM THICKNESS
2 ) : 1992
7.1 Minimum thickness of galvanized painted tower members shall be as follows: 46*2+0*615 L/r
and
Minimum Thickness, mm %axn%;?ainted Leg members, ground wire peak member and lower members of cross arms in compression 5 6
Llr
Other
members
NOTE - The values of KL/r corresponding to f a ) (vi ) and (a ) ( vii ), the following evaluation is suggested: 1 The restrained member must be connected to the restraining member with at least two bolts. 2 The restraining member must have a stiffness factor Z/L in the stress plane ( Z = Moment of inertia and L = Length ) that equals or exceeds the sum of the stiffness factors in the stress plane of the restrained members that are connected to it. 3 Angle members connected by one leg should have the holes located as close to the outstanding leg as feasible. Normal framing eccentricities at load transfer connection imply that connection holes are located between the heel of the angle end the centreline of the framing leg.
7.2 Gusset plates shall be designed to resist the shear, direct and flexural stresses acting on the weakest or critical section. Re-entrant cuts shall be avoided as far as practical. Minimum thickness of gusset shall be 2 mm more than lattice it connects only in case when the lattice is directly connected on the gusset outside the leg member. In no case the gusset shall be less than 5 mm in thickness. 8 NET SECTIONAL MEMBER AREA FOR TENSION
6.1.1 In calculating the slenderness ratio of the members, the length L should be the distance between the intersections of the centre of gravity lines at each end of the member. 6.2 Examples showing the application of the procedure given in 6.1 and 6.1.1 and method of determining the slenderness ratio of legs and bracings with or without secondary .members are given in Annex B.
NOTE - Where test and/or analysts demonstrate that any other type of bracing pattern if found technically suitable, the same can be adopted.
8.1 The net sectional area shall be the least area which is to be obtained by deducting from the gross sectional area, the area of all holes cut by any straight, diagonal or zigzag line across the member. In determining the total area of the holes to be deducted from gross sectional area, the full area of the first hole shall be counted, plus a fraction part X, of each succeeding hole cut by the line of holes under consideration. The value of X shall be determined from the formula:
X=]-
p2
where P= longitudinal spacing ( stagger ), that is the distance between two successive holes in the line of holes under consideration; transverse spacing ( gauge ), that is the distance between the same two consecutive holes as for P; and diameter of holes.
limiting
values
KL/r
shall
be
as 120
Leg members, ground wire peak member and lower members of the cross arms in compression Other members puted stresses carrying comthose
gx
200
d= 250
6.4 Slenderness ratio L/r of a member carrying axial tension only, shall not exceed 400. 3
For holes in opposite legs of angles, the value of g should be the sum of the gauges from the back of the angle less the thickness of the angle.
IS 802 ( Part
l/Set
2 ) : 1992
area of the leg of an angle shall be taken as the product of the thickness and the length from the outer corner minus half the thickness, and the area of the leg of a tee as the product of the thickness and the depth minus the thickness of the table.
9 NET EFFECTIVE AREA FOR ANGLE SECTION IN TENSION 9.1 In the case of single angle connected through one leg, the net effective section of the angle shall be taken as: A, + A,k where A, = effective ted leg, sectional area of the connecarea of the
NOTE-The
10 BOLTING 10.1 Minimum Diameter of Bolts The diameter 12 mm. of bolts shall not be less than
10.2 Preferred Sizes of Bolts Bolts used for erection of transmission line towers shall be of diameter 12, 16 and 20 mm. 10.3 The length of bolts shall be such that the threaded portion does not lie in the plane of contact of members. The projected portion of the bolt beyond the nut shall be between 3 to 8 mm. 10.4 Gross Area of Bolt For the purpose of calculating the gross area of bolts shall nornina. area of the bolt. 10.5 as d bolt, parts the shear be taken stress, as the
where lug angles are used, the effective sectional area of the whole of the angle member shall be considered. 9.2 In the case of pair of angles back to back in tension connected by one leg of each angle to the same side of gusset, the net effective area shall be taken a>: A1 ,- A, k where
A, and
in 9.1, and
k=
The bolt area for bearing shall be taken x r where d is the nominal diameter of the and t the thickness of the thinner of the jointed. be
9.3 The angles connected together back-toback ( in contact ) or separated back-to-back by a distance not exceeding the aggregate thickness of the connected parts shall be provided at pitch in line not exceeding 1 000 mm. 9.4 Where the angles are back to back but not connected as per 9.3, each angle shall be designed as a single angle connected through one leg only in accordance with 9.1. 9.5 When two tees are placed back are not connected as per 9.3, each designed as a single tee connected of a gusset only in accordance with to back but tee shall be to one side 9.2.
10.6 The net area of a bolt in tension shall taken as the area at the root of the thread. 10.7 Holes for Bolting The diameter of the hole drilled/punched not be more than the nominal diameter bolt plus I.5 mm. II FRAMJNG of
shall the
11.1 The angle between any two members common to a joint of a trussed frame shall preferably be greater than 20 and never less than 15 due to uncertainty of stress distribution between two closely spaced members.
ANNEX A ( Clause 2 )
LIST OF REFERRED IS NL). 800 : 1984 Title Code of practice for use of structural steel in general building construction ( revised) High strength structural ( second revision ) bolts 12427 : 1988 INDIAN STANDARDS IS No. 4000 : 1992 6639 : 1972 Title Code of practice for high strength bolts in steel structures Hexagonal bolt for steel structures Transmission tower bolts
3757 : 1985
B-O Example of determining the effective length of compression members of towers based on the provision given in 6.1 are given below.
B-l LEG MEMBER USING SYMMETRICAL BRACING
Slenderness Ratio KL
Concentric
loading
-$
from
0 to
120
( r
= -&
L rv;
No restraint
at ends
-$-
MEASURED
LENGTH
USING STAGGERED
BRACING
Slenderness Ratio L L
Concentric
loading
-or rxx
or 0.67 -& = Lr
from 0
'99
ko restraint at ends
L __
rxx
or&
or 0.67 -&
from 120
MEASURED
LENGTH
IS 802 ( Part l/See 2 ) : 1992 B-3 EFFECT OF END CONNECTIONS ON MEMBER CAPACITY Slenderness Ratio
Method of Loading/Rigidity of Joints Tension system with strut ( eccentricity axis ) compression in critical -&
from 0 to 120
* MEASURED LENGTH
Bracing Requirements ( Single Angle Members ) : Single triint bolt connection, at ends no res-
Multiple restraint
partial
6-4 CONCENTRIC
LOADING
TWO ANGLE
Multiple partial
bolt restraint
connection, at ends
-&
or;&
from
120 to 250 +
KL -r
= 462
+ 0.615
IS 802 ( Part l/Set 2 ) : 1992 B-5 HORIZONTAL MEMBER OF K-BRACING-TWO ANGLE MEMBER Slenderness Ratio
Method of Loading/Rigidity of Joints Tension-compression system with compression strut : Multiple bolt connection partial restraint at ends and intermediate
* MEASURED LE?K3TH
O-5 -& KL -. (. r
or-&from = 46*2+0*615
120 to 250 +
Bracing Requirements ( Two Angle Member ): Concentric load at ends, loading at intermediate directions eccentric in both 0.5 -& orFL from 0 to 120
(F
= 30 _I-0.75 Ar
at
ends
and
0.5 $KL -7
or-& =v L r
from 0 to 120
IS 802 ( Part l/Set 2 ) : 1992 B-6 EFFECT OF SUBDIVIDED PANELS FOR THE HORIZONTAL MEMBER AND END
Method of Loading/Rigidity of Joints Tension system with compression strut : Eccentricity in critical axis
Slenderness Ratio
0.5 -$ !% i
r
or-$ 3
60+0.50
Bracing Requirements : Single bolt connection, no restraint at ends for intermediate O*S-&- or&from KL --E i r L r- ) 120
to
200
Multiple bolt connection at ends. Single bolt connection at intermediate point : Partial restraint at one end, no restraint at intermediate O-5 -!?KT -= ( r L r,. from from 120 to 225 f>
28.6 + 0.762
Partial
restraint
at both ends
or & 246.2
IS 802 ( Part l/Set B-7 CONCENTRIC LOADING HORIZONTAL MEMBER TWO ANGLE MEMBER, SUBDIVIDED PANELS
2 ) : 1992
OF A
I!?n IIY+F
!
I
Slenderness Ratio
0.5 + ($L)
or-&-from
0 to 120
Concentric
or&
(E+q
E --Iv- 1
I
I
I
I
I
Multiple bolt connection at ends: Single bolt connection at intermediate joint Partial restraint at one end, no restraint at intermediate
O+
from
120 to 200 .
. E=286+0762k r
r >
Partial
>
O-5$-
or-&
-KrL =46.2+0*615; ( )
AND WITHOUT
SECONDARY
MEMBERS
Ratio Critical of:
____ or or
or CB/rvv or *ABIr,?
b)
Ll
VIEW
,4Clr,, *AD/r,\ =#
1-l
or CB/rv,.
or
B-8.3 a)
b)
or *AF/rxx or or *AC/r,,
or *AE/r,-,.
or 01
or
HIP
BRACING A
R-8.4
or or
VIEW 3-j
*Application for tension compression system only i.e. tensile stresses in one bracing to 75 percent of the the compressive stress in the other bracing. #The corner stay should be designed to provide lateral support adequately.
must
be at ienst equal
10
IS 802 ( Part l/Set 2 ) : 1992 B-9 K-BRACINGS WITH AND WITHOUT SECONDARY MEMBERS
Slenderness A Ralio Critical of:
B-9.1 B-9.2 a)
dn
i
0
AB/r,,
v MN.) ____
m
iAc
A
or or
or AWYY
b)
B-9.3 a)
m
A 0
C
b-i
4-c
-+ 0
AC/r,, CBlrvv
or
or or or or
b)
HIP A BRACING A
or or or or
AWyy
C)
or or
B-9.4
n
A
I
HIP A
AElrvv
ED/rvv DClrvv CB/ rvv
or
or or
=E
lic
.3I
VIEW 3-3
LB
#The
corner
to provide
lateral
support
adequately.
11
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Amendments
Am&d No.
Date of Issue
Text Affected
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AMENDMENT NO. 1 JANUARY 1998 TO IS 802 ( Part l/Set 2 ) : 1992 USE OF STRUCTURAL STEEL IN OVERHEAD TRANSMISSION LINE TOWERS - CQDE OF PRACTICE
PART 1 MATERIAL, LOADS AND PERMiSSlBLE Section 2 STRESSES Stresses
Permissible
3.1 Statutory requirement 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. [ Page 2, clause 54.2.2(b) ] - Correct the formula as:
FCl= 7
65 550 (b/t )
[ P&e
between
k zA$i
the following for the existing:
9.3 The angles connected together back-to-back (in contact) or separated back-to-back by a distance not exceeding the aggregate thickness of the connected parts shall be provided with sticb bolt at a pitch not exceeding 1000 mm. The slenderness ratio of individual component between adjacent stich bolts shall not be more than that of the two members together.
[ Page 10, clause B-8, Fig. 8.2(a) and 83(b) ] figures for the existing. 1
HIP BRACING
Fig. 83(b)
[ Page 10, clause B-8.3@), (b) and (c) ] other values in the last column.