IS 802 ( Part l/Set 2 ) : 1992 ( Reaffirmed 2003 ) USE OF STRUCTURAL STEEL IN OVERHEAD TRANSMISSION LINE TOWERS - CODE OF PRACTICE PART 1 MATERIAL, Section LOADS 2 AND PERMISSIBLE Stresses STRESSES Permissible ( Third Revision ) First Reprint MAY 1995 UDC 62 I *315.668.2 @ BIS 1992 BUREAU MANAK OF BHAVAN, INDIAN STANDARDS ZAFAR MARG 9 BAHADUR SHAH NEW DELHI 110002 December 1992 Price Group 6 Structural Engineering Sectional Committee, CED 7 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. IS 802 ( Part l/Sex 2 ) : 1992 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 CONDUCl'OR 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 )' when KLIr > CC IS 802 ( Part l/Set 2 ) : 1992 where c, = 77 I' TF; FY = minimum guaranteed the material, MPa E = modulus, of elasticity 2 x lo5 MPa, KL/r yield stress that of is (1) Shear Shear stress 011gross Nature of Stress Table I Ultimate Stresses in Bolts, MPa ( Clause 5.4 ) Pemirsible for Bolts of Stress Remarks of steel Property clncs C--4+ 5.6 (2) 218 (3) 31G (4) largeit effective slenderness ratio of any unbraced segment of the member, 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 Bearing stress on fo;;; diameter of Tension 436 620 Axial tensile stress 6 SLENDERNESS 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, when ( bit him < b/t Q 3781 ,/F C 1.677 _ xF E77_( b/t ) Y ( bit him I 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 b/t > 378J,;./ 7;;1;- 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 a 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 4 5 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. ...
Amiga789