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IS 802 Part l/Set 2 ) : 1992

USE OF STRUCTURAL STEEL IN OVERHEADTRANSMISSION LINE TOWERS - CODE

OF PRACTICEPART 1 MATERIAL, LOADS AND PERMISSIBLE STRESSES

Section 2 Permissible Stresses

Third Revision )First Reprint MAY 1995

UDC 62 I *315.668.2

( Reaffirmed 2003 )

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Structural Engineering Sectional Committee, CED 7

FOREWORDThis Indian Standard ( Third Revision ) was adopted by the Bureau of Indian Standards, afterthe draft finalized by the Structural Engineering Sectional Committee had been approved by theCivil Engineering Division Council.This standard has been prepared with a view to establish uniform practices for design, fabrica-tion, testing and inspection of overhead transmission line towers. Part I of the standard coversrequirements in regard to material, types of towers, loading and permissible stresses apart fromother relevant design provisions. Provisions for fabrication, galvanizing, inspection and packinghave been covered in Part 2 whereas provisions for testing of these towers have been covered inPart 3 of the standard.This standard ( Part 1 ) was first published in 1967 and subsequently revised in 1973 and 1977. Inthis revision, the code has been split in two sections namely Section 1 Materials and loads, andSection 2 Permissible stresses. Other major modifications effected in this revision ( Section 2 )are as under:

a) Permissible stresses in structural members have been given in terms of the yield strengthof 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.b) Critical stress in compression Fcr has been modified for width/thickness ratio of theangles exceeding the limiting value for calculating the allowable unit compressivestresses.c) Effective slenderness ratios ( K L/ r for redundant members have been included andprovisions further elaborated.d) Examples for the determination of slenderness ratios have been extended to include Kand x bracings with and without secondary members.

Designs provisions or other items not covered in this standard shall generally be in accordancewith 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 inview. Assistance has also been derived from the &Guide for design of steel transmission linetowers ( second edition ) - ASCE Manual No. 52, issued by American Society of Civil Engineers( ASCE ) hew York, 1988.For the purpose of deciding whether a particular requirement of this Code is complied with, thefinal value, observed or calculated, expressing the result of a test, shall be rounded off in accor-dance with IS 2 : 1960 Rules for rounding off numerical values ( revised . The number ofsignificant places retained in the rounded off value should be the same as that of the specified

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IS 802 Part l/Sex 2 ) : 1992

I ndian St andardUSE OF STRUCTURAL STEEL IN OVERHEAD

TRANSMISSION LINE TOWERS - CODEOF PRACTICE

PART 1 MATERIAL, LOADS AND PERMISSIBLE STRESSESSection 2 Permissible Stresses

( Third Revi si on1 SCOPE1.1 This standard ( Part l/Set 2 ) stipulates thepermissible stresses and other design parametersto be adopted in the design of self-supportingsteel lattice towers for overhead transmissionlines.1.1.1 Materials, type of towers, loading andbroken wire conditions are covered in Section 1of this standard.1.1.2 Provisions on fabrication and testing oftransmission line towers have been covered inPart 2 and Part 3 respectively of the standard.

NOTE - While formulating the provisions of thisstandard it has been assumed that the structuralconnections are through bolts.1.2 This standard does not cover guyed towers.These will be covered in a separate standard.2 REFERENCESThe Iudian Standards listed in Annex A arenecessary adjuncts to this standard.3 STATUTORY REQUIREMENTS3.1 Statutory requirement as laid down in theI ndian Electri cit y Rul es. 1956 or by any otherstatutory code applicable to such structuresshall be followed.3.2 Compliance with this code does not relieveany one from theresponsibilityof observing localand state byelaws, fire and safety laws and othercivil aviation requirements applicable to such

exceed the following percentage of the ultimatestrength of the conductor:Initial unloaded tension 35 percentFinal unloaded tension 25 percent

provided that the ultimate tension under every-day temperature and full wind or minimumtemperature and two-thirds wind pressure doesnot exceed 70 percent of the ultimate tensilestrength of the cable.5 PERMISSIBLE STRESSES5.1 Axial Stresses in TensionThe estimated tensile stresses on the net effec-tive sectional areas ( see 9 ) in various members,shall not exceed minimum guaranteed yieldstress of the material. However in case theangle section is connected by one leg only, theestimated tensile stress on the net effectivesectional area shall not exceed FY ,where F, isthe minimum guaranteed yield stress of thematerial.5.2 Axial Stresses in Compression5.2.1 The estimated compressive stresses invarious members shall not exceed the valuesgiven by the formulae in 5.2.2.5.2.2 The allowable unit stress F,, in MPa onthe gross cross sectional area of the axiallyloaded compression members shall be:

a) F*=[l-f(+$-)a]xF,

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IS 802 Part l/Set 2 ) : 1992where

c, = 77 I TF;FY = minimum guaranteed yield stress ofthe material, MPaE = modulus, of elasticity of steel that is2 x lo5 MPa,

KL/r - largeit effective slenderness ratio ofany unbraced segment of the member,L = unbraced length of the compressionmember ( see 6.1.1 ) in cm, andr z appropriate radius of gyration in cm.

5.2.2.1 The formulae given in 5.2.2 are appli-cable provided the largest width thickness ratiob/t is not more than the limiting value givenby:

whereb=t =

-( b/t )lim =z 210/i/ Fy

distance from edge of fillet to theextreme fibre in mm, andthickness of flange in mm.

5.X2.2 Where the width thickness ratio exceedsthe limits given in 5.2.2.1, the formulae givenin 5.2.2 shall be used substituting for &. thevalue F,, given by:a) Fe, = C .677 _ E77_ b/t )bit him I x F

anu,when ( bit him < b/t Q 3781 ,/F

b) Fe, = 65 550b,t )_ when b/t > 378J,;./ 7;;1;-NOTE - The,maximum permissible value of b/lr forany type of steel shall not exceed 25.

5.3 The redundant members shall be checkedindividually for 2.5 percent of axial load carriedby the member to which it supports.5.4 Stresses in BoltsUltimate stresses in bolts conforming to pro-perty class 4.6 of IS 6639 : 1972 and to propertyclass 5.6 of IS 12427 : 1988 shall not exceed the

Table I Ultimate Stresses in Bolts, MPaClause 5.4 )

Nature of Stress Pemirsible Stress Remarksor Bolts ofProperty clncs

C--4+ 5.61) 2) 3) 4)Shear

Shear stress 011gross 218 31Garea of bolts For gross areaof bolts ( see10.4). For boltsin double shearthe area to beassumed shallbe twice thearea definedBearingBearing stress on 436 620 For the boltfo;;; diameter of area in bearingsee 10.5 )TensionAxial tensile stress 194 2.50 -6 SLENDERNESS RATIOS6.1 The slenderness ratios of eompression andredundant members shall be determined asfollo\vs:

Type of Members Value of KL] ra) Compression Members

i) Leg sections or jointmembers bolted in bothfaces at connections for0 c L/r Q 120ii) Members with concentricloading at both ends ofthe unsupported pane1for 0 < L/r c 120

iii) Member with concentricloading at one end andnormal framing eccen-tricity at the other endof the unsupported panelfor 0 c Ljr c 1.20

Ll r

L l r

30 -0.75 L/r

iv) Member with normalframing eccentricities at 60 + 0.50 L/t

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vi)

vii)

Member partially res-trained against rotationat one end of the unsup-ported panel fnr 120

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IS 802 ( Part l/Set 2 ) : 19929 NET EFFECTIVE AREA FOR ANGLESECTION IN TENSION9.1 In the case of single angle connectedthrough one leg, the net effective section of theangle shall be taken as:

A, + A,kwhere

NOTE-The area of the leg of an angle shall betaken as the product of the thickness and the lengthfrom the outer corner minus half the thickness, andthe area of the leg of a tee as the product of thethickness and the depth minus the thickness of thetable.

10 BOLTING10.1 Minimum Diameter of Bolts

A, = effective sectional area of the connec- The diameter of bolts shall not be less thanted leg, 12 mm.A, := the gross cross-sectional area of thetmconnecred leg, andk _ 3ArA, + A,

10.2 Preferred Sizes of BoltsBolts used for erection of transmission linetowers shall be of diameter 12, 16 and 20 mm.

where lug angles are used, the effective sec-tional area of the whole of the angle membershall be considered.9.2 In the case of pair of angles back to backin tension connected by one leg of each angleto the same side of gusset, the net effective areashall be taken a>:

10.3 The length of bolts shall be such that thethreaded portion does not lie in the plane ofcontact of members. The projected portionof the bolt beyond the nut shall be between3 to 8 mm.10.4 Gross Area of Bolt

whereA1 ,- A, k

For the purpose of calculating the shear stress,the gross area of bolts shall be taken as thenornina. area of the bolt.A, and A, arc as deiinzd in 9.1, andk= -_._%r-.-5A, + A,

10.5 The bolt area for bearing shall be takenas d x r where d is the nominal diameter of thebolt, and t the thickness of the thinner of theparts jointed.9.3 The angles connected together back-to-back ( in contact ) or separated back-to-backby a distance not exceeding the aggregate thick-ness of the connected parts shall be providedat pitch in line not exceeding 1 000 mm.

10.6 The net area of a bolt in tension shall betaken as the area at the root of the thread.10.7 Holes for Bolting

9.4 Where the angles are back to back but notconnected as per 9.3, each angle shall be design-ed as a single angle connected through one legonly in accordance with 9.1.9.5 When two tees are placed back to back butare not connected as per 9.3, each tee shall bedesigned as a single tee connected to one sideof a gusset only in accordance with 9.2.

The diameter of the hole drilled/punched shallnot be more than the nominal diameter of thebolt plus I.5 mm.II FRAMJ NG11.1 The angle between any two memberscommon to a joint of a trussed frame shallpreferably be greater than 20 and never lessthan 15 due to uncertainty of stress distribu-tion between two closely spaced members.

ANNEX AClause 2 )

LIST OF REFERRED INDIAN STANDARDS

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ANNEX 33( Clause 6.2 )

EXAMPLES OF DETERMLNATiON OF

IS 802 ( Part l/Set 2 ) : 1992

&LENDERNESS RATIOSB-O Example of determining the effective length of compression members of towers based on theprovision given in 6.1 are given below.B-l LEG MEMBER USING SYMMETRICAL BRACING

M et hod of Loading/Rigidi t y of JointsSlenderness Ratio

Concentric loading -$ from 0 to 120 - = -&(KLr

No restraint at ends -$- Lrv;

* MEASURED LENGTHB-2 LEG MEMBER USING STAGGERED BRACING

M et hod of Loading/Rigidi t y of JointsConcentric loading

ko restraint at ends L__ or& or 0.67 -& from 120rxx

Slenderness RatioL L-or -rxx 99 or 0.67 -& from 0

L-r

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IS 802 Part l/See 2 ) : 1992B-3 EFFECT OF END CONNECTIONS ON MEMBER CAPACITY

* MEASUREDLENGTH

Method of Loading/Rigidi tyof Joint sTension system with compressionstrut ( eccentricity in criticalaxis )

Bracing Requi rement s ( Si ngle AngleMembers ) :Single bolt connection, no res-triint at ends

Multiple bolt connection partialrestraint at both ends

6-4 CONCENTRIC LOADING TWO ANGLE MEMBERMethod of Loading/Rigidityof Joints

Tension system strut com-pression concentric loading

Bracina Reaui rement s ( Tw oAngle kfem6er ) :Single bolt connection, norestraint at ends

Slenderness Ratio

-& from 0 to 120

7Lz from 120 to 200KL

(-- =L

--r r

A- from 120 to 250rvvKL--= 46.2 + 0.615r +

Slenderness RatioL--rxx or-r& from 0 to 120KL L

(--.- = - r

L-.-rxx or-rJ& from 120 to 200KL L

(_ = --r

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IS 802 ( Part l/Set 2 ) : 1992B-5 HORIZONTAL MEMBER OF K-BRACING-TWO ANGLE MEMBER

* MEASURED LE?K 3TH

M ethod of Loading/Rigidi tyof Joi nt sTension-compression system w i t hcompressi on st rut :Multiple bolt connection partialrestraint at ends and interme-diate

Bracing Requir ement s ( Tw o Angl eM ember ):Concentric load at ends, eccentricloading at intermediate in bothdirections

Concentric loading at ends andintermediate

Slenderness Ratio

O-5 -& or-&from 120 to 250

(.KL-. r = 46*2+0*615 +

0.5 -& orFL from 0 to 120

( F = 30 _I- 0.75 A- 1

0.5 - or-& from 0 to 120KL L-7 =v r

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IS 802 ( Part l/Set 2 ) : 1992B-6 EFFECT OF SUBDIVIDED PANELS FOR THE HORIZONTAL MEMBER AND ENDCONNECTIONS ON MEMBER CAPACITY

* MEASUREDLENGTH M ethod of Loading/Rigidityof Joint sTension system w i t h compres-sion strut :

Eccentricity in critical axis

Bracing Requirements :Single bolt connection, norestraint at ends for inter-mediate

Multiple bolt connection atends. Single bolt connectionat intermediate point :Partial restraint at one end,no restraint at intermediate

Partial restraint at both ends

Multiple bolt connectionPartial restraint at ends andintermediate

Slenderness Ratio

0.5 -$ or-$ from 0 to 120

i % 3 60+0.50 -mkr r

O*S-&- or&from 120 to 200

iKL L--Er r- )

O-5 - ?- from 120 to 225 -

(KT-=r 28.6 + 0.762 f- >Lr,. from 120 to 250KL-=r 46.2 + O-615 -5

0.5% or & from 120 to 250KL-~-r 246.2 + 0.615 4

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IS 802 ( Part l/Set 2 )B-7 CONCENTRIC LOADING TWO ANGLE MEMBER, SUBDIVIDED PANELS OF AHORIZONTAL MEMBER

X

II- ?nY+FyIX

II

EI --Iv-II

1

Method of LoadingjRi gidi t yof PanelTension system w it h compres-sion st rut :

Concentric loading

Bracing Requirements:Single bolt connection, norestraint at ends and inter-mediate

Multiple bolt connection atends: Single bolt connectionat intermediate jointPartial restraint at one end,no restraint at intermediate

Partial restraint at both ends

Multiple bolt connectionPartial restraint at ends andintermediate

: 1992

Slenderness Ratio

0.5 + or-&-from 0 to 120($L)

0. 5 - or& from 120 to 200(E+q

O+ from 120 to 200

( E=286+0762k.r r >

A- from 120 to 250rxxKL-= 46*2+0.615 +r >

O- 5 - or-& from 120 to 250

( KrL =46.2+0*615;- )

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IS 802 f Part 1Kec 2 ) : 1992B-8 X-BRACINGS WITH AND WITHOUT SECONDARY MEMBERS

B-8.1

B-8.2a)

b)

B-8.3a)

b)

a

R-8.4

Sl enderness Rati o Crit ical of:

__.-- ~__.._~_.. _ ____AC/r,,- or CB/rvv orAB/r,, or *ABIr,? orAD/r,,

L l =#VIEW 1-l

,4Clr ,, or CB/rv ,. or*AD / r,\

AD / r\ - , r *AF/rxx orDC/rv v or *AE/r,-,. 01CBlrvv rAC/rxx r *AC/r,,

ADl rvv r *AF/rxx orDC/rxrv orCBjrvv or *AE rv \

HIP BRACINGA A AE/rvv oc *AF/rxx or

ED/r or *AE/rvv orDC/rvV or CBlrvv

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IS 802 Part l/Set 2 ) : 1992B-9 K-BRACINGS WITH AND WITHOUT SECONDARY MEMBERS

B-9.1

B-9.2a)

b)

B-9.3a)

b)

C)

B-9.4

An i 0

mAc 0Ab-i-c -+0AmC 0A

In\ = E0lic .3I

Slenderness Ral io Crit ical of:AB/r,,

v MN.) ____AC rov orCB/rrv orABIr,, or AWYY

HIP BRACINGA A

VIEW 2-2HIP BRACING

A A

AC/r,,CBlrvvor

AD/r,, orDC/rvv orCB/rvv orABlrxx or

AD/r,, orDC/r, orCB/ryv orA C/r,* or AWyy

AD/r, orDCjrvv orCBIr,V

AElrvv orED/rvv orDClrvv orCB/ rvv

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BIS is a statutory institution established under the Bur eau cfhdim Stumfmis Act, 1986 to promoteharmonious development of the activities of standardization, marking and quality certification of goodsand attending to connected matters in the country.CopyrightBIS has the copyright of all its publications. No part of tnese publications may be reproduced in any formwithout the prior permission in writing of BIS. This does not preclude the free use, in the course ofimplementing the standard, of necessary details, such as symbols and sizes, type or grade designations.Enquiries relating to copyright be addressed to the Director (Publications), BIS.Review of Indian StandardsAmendments are issued to standarLjas the need arises on the basis of comments. Standards are alsoreviewed periodically; a standard along with amendments is reaffirmed when such review indicates thatno changes are needed; if the review indicates that changes are needed, it is taken up for revision. Usersof Indian Standards should ascertain that they are in possession of the latest amendments or edition byreferring to the latest issue of BIS Handbook and Standards Monthly Additions.This Indian Standard has been developed from Dot : No. CED 7 ( 4725 )

Amendments Issued Since PublicationAm&d No. Date of Issue Text Affected-

BUREAU OF INDIAN STANDARDSHeadquarters:Manak Bhavan, 9 Bahadur Shah Zafar Marg, New Delhi 110002 Telegrams : ManaksansthaTtilephones : 33101 31,331 13 75 (Common to all offices)Regional Offices :Central : Manak Bhavan, 9 Bahadur Shah Zafar MargNEW DELHI llooO2Eastern : 1114 C. I.T. Scheme \II\J,M, V. I. P. Road, ManiktolaCALCUTTA 7OOQ54

Telephone1 3310131331 13 75

37 84 99,37 85 61378626,378662

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AMENDMENT NO. 1 JANUARY 1998TOIS 802 Part l/Set 2 ) : 1992 USE OFSTRUCTURAL STEEL IN OVERHEAD TRANSMISSIONLINE TOWERS - CQDE OF PRACTICE

PART 1 MATERIAL, LOADS ANDPERMiSSlBLE STRESSES

Section 2 Permissible Stresses( Third Revision )

(Page 1, clause 3.1 ) - Substitute the following for the existing:3.1 Statutory requirement as laid down in the Indian Electricity Rules, 1956 orby any other statutory body applicable to such structures as covered in thisstandard shall be satisfied.

[ Page 2, clause 54.2.2(b) ] - Correct the formula as:65 550 b 378FCl= 7 when - >--(b/t ) RG?

[ P e 2, clause &l(a) (ii), (iii), (iv) and (v) ] - Substitute 6 for

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Amend No. 1 to IS 802 Part l/Set 2) : 1992

Fig 8.2 a)

HIP BRACINGFig. 83 b)

[ Page 10, clause B-8.3@), b) and c) ] - Insert or EF/rw along withother values in the last column.