IS 6533 (Part 2) : 1989(Reaffirmed 1998)

Edition 2.1(1998-06)

Indian Standard

CODE OF PRACTICE FOR DESIGN ANDCONSTRUCTION OF STEEL CHIMNEY

PART 2 STRUCTURAL ASPECT

( First Revision )(Incorporating Amendment No. 1)

UDC 697.8 (669.14) : 69.001.3

© BIS 2002

B U R E A U O F I N D I A N S T A N D A R D SMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

Price Group 8

Structural Engineering Sectional Committee, CED 7

FOREWORD

This Indian Standard (Part 2) (First Revision) was adopted by the Bureau of Indian Standards on20 April 1989, after the draft finalized by the Structural Engineering Sectional Committee hadbeen approved by the Civil Engineering Division Council.This standard was first published in 1971. On suggestions by practising engineers andrepresentatives of various organizations in the country, the Sectional Committee decided tobifurcate the standard in two parts, separating structural aspects from the mechanical aspects asfollows:

Part 1 Mechanical aspects, andPart 2 Structural aspects.

In this part (Part 2), the dynamic effects of wind have been included as a check for resonanceoscillations. More accurate method of determining the natural frequency of oscillation has beenincluded. Many of the commonly known formulae and calculation steps for design have beendeleted to make the code concise. Further, since the principal load on the chimney is wind load, noincrease in permissible stress is envisaged in this code aligning with the present line of thinkingfor wind loads.Atmospheric pollution regulations necessitate adoption of tall chimneys which requirestrengthening against stresses caused by oscillation due to wind action. Alternative procedures(a) making an appropriate increase in the design wind loading, and (b) indicating the need ofstrengthening or incorporation of devices for suppressing von-Karman type oscillations are givenin Annex A.Certain methods of strengthening, such as welding or bolting helical strakes to the top one-thirdheight of the chimney and the installation of damping devices are recommended ( see A-2.2 ).Design and construction of chimneys have become specialized field with a lot of scope for researchand modifications. It is, therefore, attempted in this standard to cover only the basic requirements.The designer should use his discretion in the use of research data available.In the preparation of this standard, considerable assistance has been derived from the following:

a) BS 4076 : 1978 Specification for steel chimneys, andb) Stroitelny Normi E Provila (SNIP-II-VI-1974) USSR (Soviet Norms on Loads and Actions).

This edition 2.1 incorporates Amendment No. 1 (June 1998). Side bar indicates modification of thetext as the result of incorporation of the amendment.

IS 6533 (Part 2) : 1989

1

Indian Standard

CODE OF PRACTICE FOR DESIGN ANDCONSTRUCTION OF STEEL CHIMNEY

PART 2 STRUCTURAL ASPECT

( First Revision )1 SCOPE

1.1 This standard (Part 2) covers terminology,loading, materials, structural design,construction, inspection, maintenance andpainting of both self-supporting and guyed steelchimneys (with or without lining) and theirsupporting structures.

1.2 The design of chimneys of cross section otherthan circular is not included in this standard.

1.3 Chimneys in pairs, rows or groups, and thosenear other structures of comparable height maybe subjected to exceptional wind force andparticularly wind induced oscillations greaterthan that allowed for in this standard.Appropriate expert advice should, therefore, beobtained in these cases.

1.4 The purpose for which the chimney isrequired will determine whether lining,insulation or cladding is necessary.

2 REFERENCES2.1 The Indian Standards listed in Annex B arenecessary adjuncts to this standard.

3 STATUTORY PROVISIONS3.1 Compliance with this code does not relieveany one from the responsibility of observingprovisions as may have been promulgated byany statutory body and/or observing provincialbuilding byelaws and the civil aviationrequirements pertaining to such structures.

4 TERMINOLOGY

4.0 For the purpose of this standard, definitionsgiven in 4.1 to 4.40 shall apply.

4.1 Access DoorA door for the entry of personnel.

4.2 Access HooksFittings welded to a chimney to permit theattachment of steeplejack’s equipment.

4.3 Access LadderA steel ladder provided along the height of thechimney fixed with chimney shell for providingaccess for personnel to reach different heights forinspection/maintenance, etc.

4.4 Aerodynamic Stabilizer

A device fitted to the structural shell to reducewind excited oscillations by modifying vertexsheddings.

4.5 Anchor for Guy

The foundation for the fixing of guy.

4.6 Base Gussets

A triangular or trapezoidal steel plate fixed tothe chimney shell and to the base plate.

4.7 Base Plate

A horizontal steel plate fixed to the base of achimney.

4.8 Base Stool

A construction comprising two vertical plates(base gussets) welded to the chimney shell andto the base plate, supporting a horizontal platethrough which the holding down bolts pass andagainst which the bolts can be tightened.

4.9 Bracket

A construction providing resistance to lateraldisplacement of the chimney, and/or supportingpart or all of the weight of the chimney.

4.10 Bracketed Chimney

A chimney in which not all external appliedloads (namely, wind) are carried exclusively bythe structural shell and for which brackets areprovided to ensure stability.

4.11 Clean Out Door

A door, normally at the base of the chimney, topermit the removal of flue dust and/or provideaccess.

4.12 Cope Band

A steel flat or angle attached to the top of thechimney around its perimeter to give addedstrength and corrosion resistance at this level.

4.13 Cope-Hood

A hood fitted externally to the top of a liner,covering the upstand of the cap plate to preventthe ingress of rain water.

IS 6533 (Part 2) : 1989

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4.14 Corrosion Test Piece

A fixed or removable steel plate insert,generally of lesser thickness than the shell ofthe chimney, in contact with the waste gasesand fitted at strategic points where maximumcorrosion is expected to occur.

4.15 Cowl

A conical or dished cap fitted to the top of thechimney to prevent or minimize entry of rainwater.

4.16 Cowl Stays

Steel stays which connect the cowl to the top ofthe chimney.

4.17 Cravat

An upstand fixed to the roof of a building orroof plate to prevent the entry of rain waterinto the building.

4.18 Double Skin Chimney

A chimney consisting of an outer load-bearingsteel shell and all inner steel liner whichcarries the flue gases.

4.19 Doubling Plate

A plate fixed to the shell to reinforce it whereincreased stresses occur.

4.20 Flare

The bottom portion of the chimney in the formof a truncated cone.

4.21 Gallery

The platform around the shaft for observationand maintenance.

4.22 Guy

A wire rope attached at one end of the chimneyand anchored at the other end so as to provideresistance to the lateral displacement of the topof the chimney.

4.23 Guy Band

A steel band/section fitted around the outside ofa chimney with provision for the attachment ofguys.

4.24 Guyed Chimney

A chimney in which not all externally appliedloads (namely, wind) are carried exclusively bythe structural shell and for which guys areprovided to ensure stability.

4.25 Height of Steel Shaft

Length between underside of base plate and thetop of the chimney.

4.26 Holding Down Bolts

Bolts built into a concrete foundation orsupporting framework to provide anchorage atthe base of the chimney.4.27 Inlet

An opening in the side of a chimney to permitthe entry of exhaust gases from connecting flueduct.

4.28 Joint Flange

A steel section fitted to the end of a chimneysection to enable section to be connectedtogether.

4.29 Lateral Supports

Supports positioned at appropriate levelswithin the structural shell to locate the linersand to allow for their independent expansion.

4.30 Liners

Flue ducts contained within a structural shell.

4.31 Multiflue Chimney

A group of two or more chimneys within astructural framework or a group of two or moreliners within a structural shell.

4.32 Nominal Chimney Diameter

Internal diameter at the top of the steel shell.

4.33 Roof Plate

A plate which follows the contour of the rootround the chimneys where it passes throughthe roof. It is also known as flashing around thechimney.

4.34 Self-Supporting Chimney

A chimney in which externally applied loads(namely, wind) are carried exclusively by thestructural shell and which together with thefoundation, will remain stable under all designconditions without additional support.

4.35 Stack

Normally the straight portion of the chimney.

4.36 Stay

A rigid member providing both tensile andcompressive resistance to the lateraldisplacement of the chimney.

4.37 Stayed Chimney

A chimney in which not all externally appliedloads (namely, wind) are carried exclusively bythe structural shell and for which stays areprovided to ensure stability.

4.38 Strake Vane

An aerodynamic stabilizer fitted to reduce windexcited oscillations.

IS 6533 (Part 2) : 1989

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4.39 Structural Shell

The main external steel plate of the chimneyexcluding any flanges.4.40 Weather Hood

A hood designed to shed rain water clear of thecravat and prevent its entry into the building.

5 MATERIALS

5.1 Plates and Sections

Steel plates and sections used in theconstructions of chimneys shall conform toIS 226 : 1975, IS 961 : 1975, IS 2062 : 1984 orIS 8500 : 1977, whichever is appropriate.Suitable stainless or alloy steels may be used inspecial circumstances, such as, when the gasesare of an extremely aggressive nature or are ata temperature higher than 480°C but thethickness shall otherwise comply with therequirements of this specification.5.2 Rivets

Rivets used in the constructions of chimneysshall comply with IS 1929 : 1982, andIS 2155 : 1982, as appropriate. Rivets made ofhigh tensile steel, if used, shall conform toIS 1149 : 1982.5.3 Welding Consumables

5.3.1 Covered electrodes shall conform toIS 814 (Part 1) : 1974, IS 814 (Part 2) : 1974 orIS 1395 : 1982, as appropriate.5.3.2 The bare wire electrodes for submergedarc welding shall conform to IS 7280 : 1974.The combination of wire and flux shall satisfythe requirements of IS 3613 : 1974.5.3.3 Filler rods and bare electrodes for gassheilded metal arc welding shall conform toIS 6419 : 1971 and IS 6500 : 1972, asappropriate.5.4 Bolts and Nuts

Bolts and nuts shall conform to IS 1363 : 1984,1364 : 1983, IS 3640 : 1982, IS 3757 : 1972,IS 6623 : 1972, IS 6639 : 1972, and IS 7002 :1972 as appropriate. Foundation bolts shallconform to IS 5624 : 1970.5.4.1 Supply conditions of threaded fastenersshall conform to IS 1367 (Part 1) : 1980, IS 1367(Part 3) : 1979 and IS 1367 (Part 6) : 1980, asappropriate.5.5 Washers

Washers shall conform to IS 5369 : 1975,IS 5370 : 1969, IS 6610 : 1972 and IS 6649 :1972, as appropriate.5.6 Steel Castings

Steel castings shall conform to Grade 23-45 ofIS 1030 : 1982.

5.7 Guy Ropes and Fittings

Guy ropes shall conform to IS 2141 : 1979 andIS 2266 : 1970 and shall be galvanized orprotected from corrosion by other suitablemeans.

5.8 Other materials used in association withsteel works shall, where appropriate IndianStandard Specification for the material exist,conform to such specification.

6 LOADING AND LOAD COMBINATIONS

6.1 Dead Loads

Where the unit weight of materials are notknown, the dead load shall be calculatedaccording to IS 875 (Part 1) : 1987.

6.1.1 In calculating dead loads, the weight ofchimney shell, permanent fixtures such as,ladders, platforms, baffles, and guys (if any)shall be included. The weight of flue liningshall be treated as a separate load for thepurpose of load combinations. The flue liningshall not be assumed to increase sectionmodulus of the shell nor resist overturning dueto its lateral bending stiffness or struttingaction.

6.2 Imposed Loads

Imposed loads on platforms shall be taken atthe rate of 300 kg/m2.

6.3 Wind Loads

The wind loads shall be calculated inaccordance with the provisions contained inIS 875 (Part 3) : 1987.

6.3.1 Wind force on ladders and other fixturesfixed to a chimney shall be determined andadded to the force on the chimney.

6.4 Earthquake Loads

Unless otherwise specified, the provisioncontained in IS 1893 : 1975 shall apply.

6.5 Load Combination

For the design of chimney and its foundation,any of the following load combinations whichproduce maximum forces and effects andconsequently maximum stresses shall bechosen:

a) Dead load + wind load,

b) Dead load + earthquake load,

c) Dead load + load due to lining + imposedload on service platforms + wind load, or

d) Dead load + load due to lining + imposedload on service platforms + earthquakeloads.

IS 6533 (Part 2) : 1989

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7 DESIGN7.1 General

For the design of chimney shell and othercomponents of chimney in steel, the relevantprovisions contained in IS 800 : 1984 shall beapplicable in conjunction with the provision ofthis standard.7.1.1 The provisions covered in IS 800 : 1984regarding the following shall, however, besuperseded by the requirements of thisstandard:

a) Minimum thickness,b) Allowable deflection,c) Allowance for corrosion,d) Allowance for temperature,e) Allowable compressive stress in circular

shells due to direct force and bendingmoment, and

f) Stresses due to earthquake.7.2 Basic Dimensions

7.2.1 The basic dimensions of the chimney,namely, clear diameter, height, etc, are decidedon considerations of temperature, compositionof flue gases, adjacent structures, pollutioncontrol, draft requirements, etc, with Part 1 inaccordance with this standard. Nevertheless,certain recommended proportions should bemaintained for the strength and stability of thechimney.7.2.2 The clear diameter of the chimney is thenominal diameter of the shell if the chimney isunlined or partially lined. For fully linedchimney the clear diameter shall be the cleardiameter of the lining at the top. The fully linedchimney shall have a minimum clear diameterof 500 mm. If, for technological reasons, it isnecessary to have a smaller diameter, the topopening shall be reduced by constricting thepassage locally.7.2.3 A self-supporting chimney of height 40 mand above shall be provided with a flare at thebase to achieve better stability.7.2.4 Proportions of the basic dimensions of aself-supporting chimney shall conform to thefollowing:

a) Minimum height of flare be equal toone-third the height of the chimney.

b) Minimum outside diameter of unlinedchimney shell at top be equal toone-twentieth of the height of cylindricalportion of chimney and for lined chimneyit shall be one-twentyfifth of the height ofthe cylindrical portion.

c) Minimum outside diameter of flaredchimney shell at base be equal to 1.6 timesthe outside diameter of chimney shell attop.

7.3 Minimum Thickness of Steel

7.3.1 Chimney ShellThe minimum thickness of the structuralchimney shell in single or multiple shellconstructions, shall be the calculated thicknessobtained from stress and deflectionconsiderations plus the corrosion allowance( see 7.5 ), but shall not be less than 6.0 mm norless than 1/500 of the outside diameter of thechimney at the considered height.

7.3.2 Chimney LinerThe minimum thickness of the steel liner in adouble skin or multiple construction shall bethe calculated thickness obtained from stressconsiderations plus the corrosion allowance,but shall be not less than 6.0 mm.

7.3.3 Supporting SteelworkThe minimum thickness for hot rolled sectionsused for external construction exposed to theweather shall be 8.0 mm, and for constructionsnot so exposed and ancillary steelwork, 6.0 mm.These provisions do not apply to the webs ofIndian Standard rolled steel sections or topackings. The minimum thickness of hollowsections sealed at the ends, used for externalconstructions exposed to the weather or othercorrosive influences shall be 4 mm, and forconstructions not so exposed shall be 3 mm.

7.3.4 Angle FlangesThe minimum thickness of jointing flanges tochimney shall be 6.0 mm.

7.4 Allowable Deflection

The maximum deflection at the top of the steelchimney produced by the wind load withouttaking into account the dynamic factors,calculated as acting on the circular crosssection shall not be greater than h/200. Where‘h’ is the unsupported height of the chimney.

7.5 Allowance for Corrosion

The total allowance for corrosion shall be thesum of the external ( Tce ) and internal ( Tci )allowances given in Table 1. This totalallowance shall be added to the thickness ofshell obtained from the calculations of thestresses and deflection. Internal flanges shallhave corrosion allowance Tci , and externalflanges corrosion allowance Tce except if theyare encased.

NOTE — However, a lower corrosion allowance thanspecified in Table 1 may be adopted at the discretion ofthe designer/owner, if it can be ensured that theproperties of flue gas and its effect on the chimney shellwill not adversely affect the safety requirements.

7.6 Effective Height of Chimney Shell

Effective height of chimney shall be as specifiedin Table 2.

IS 6533 (Part 2) : 1989

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Table 1 Corrosion Allowance Tce and Tci,( Clause 7.5 )

Degree of Corrosion Expected Corrosion Allowance, in mm

Copper Bearing Steel Non-copper Bearing Steel

Design Life Design Life

10 yrs 20 yrs 10 yrs 20 yrs

a) External, Tce1) None (that is, paint, insulation, cladding or

similar protection available always)2) Above average (that is, unprotected)

Nil

1

Nil

2

Nil

1.5

Nil

3

b) Internal, Tci1) None (such as, non-corrosive flue gases or the

structural shells of multiflue chimney)2) Average (such as, lined, insulated or natural

gas fired)3) Above average (such as, unprotected coal fired)

Nil

1

2

Nil

2

3

Nil

1.5

3

Nil

3

5

NOTES1 The internal corrosion allowance for the exceptional degree of corrosion shall be as mutually agreed between thepurchaser and the designer, based on the desired life of the chimney.2 No corrosion allowance need be provided if the chimney shell is made of stainless steel.3 Partly lining the inside chimney with stainless steel does not eleminate the possibility of corrosion because of thecondensed effluent passing down to chimney. The same is not recommended.

Table 2 Effective Height of Chimney Shell( Clauses 7.6 and C-1 )

Description Effective Height, he

Self-supporting chimney

he = a

Supported chimney,fixed base

For stresses in BChe = bFor stresses in ABhe = 0.85 a

Supported chimney, pinned based

For stresses in BChe = bFor stresses in ABhe = a

IS 6533 (Part 2) : 1989

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7.7 Maximum Permissible Stress in the Shell

To control buckling, the compressive stresscaused by the combination of extreme fibrestresses due to bending and direct load for theload combination given in 6.5, shall not exceedvalues specified in Table 3 for steels conformingto IS 226 : 1975 and IS 2062 : 1984. The valuesshall be reduced further if necessary fortemperature and calculated with the corrosionallowance deduced from the thickness t.7.7.1 For steels other than IS 226 : 1975 andIS 2062 : 1984, maximum permissible stressesshall be obtained by multiplying the values inTable 3 by the factor Fy / fy, where Fy is theguaranteed yield stress of steel used and fy isthe guaranteed yield stress of steel conformingto IS 226/IS 2062, that is, 250 MPa.7.7.2 The maximum permissible stresses givenin Table 3 have been worked out in accordancewith the formulae given in Annex C.7.8 Allowance for Temperature

7.8.1 Maximum permissible stresses asobtained in 7.7 shall be corrected for the mostadverse temperature conditions to which themember or part may reasonably be expected tobe exposed by multiplying with the appropriatetemperature coefficient Kt given in Table 4. Theexpected temperature of steel components shallnot be allowed to exceed 400°C.

In case of steels other than IS 226 : 1975 andIS 2062 : 1984, maximum permissible stressesas obtained from 7.7.1, shall be reduced basedon temperature coefficient factor Kt obtained bydividing yield stress at the operatingtemperature by the yield stress at 20°C.

7.9 Other Stresses in Steel

Allowable stresses in axial tension, shear andbearing shall be as specified in IS 800 : 1984.

7.10 Increase in Stresses

For load combination involving earthquake, thepermissible stresses may be exceeded by 33percent provided the steel thickness shallneither be less than the minimum thicknessspecified nor when the earthquake loads areneglected.

7.11 Allowance for Large Openings in shell

The allowable stresses apply to the shell platesafter due allowance for rivets and bolt holes.Where large apertures are cut in the shellplates, as for inlets or inspection panels, astructural analysis of the stresses shall bemade and compensating material provided, asrequired, to ensure that the stresses specifiedin the standard are not exceeded. Apertures inthe shell plates, other than flue inlets, shallhave the corners rounded to a minimum radiusof 10 t, where t is the thickness of the plate.

13---

Table 3 Maximum Permissible Stress for Circular Chimneys( Clauses 7.7, 7.7.1, 7.7.2 and C-1 )

Maximum Permissible Stress in MPa, for D/t

140andless

150 160 170 180 190 200 225 250 300 350 400 450 500

Up to 2030405060708090

100110120130140150

126108

897259484033282421181614

124107

887158484033282421181614

123105

867057473933282420181514

120103

856956463832272320171513

118101

836855453731262319171513

11599816654443731262219171513

11296796452433630252219161413

10590746049403328242017151312

9985705746383126221916141211

8775625041332823201714131110

78675545363025211815131110

9

706050403327221916131210

98

6455453730242017141211

987

5850413427221916131110

877

t = thickness of the plate of the level considered,D = mean diameter at the level considered (in metres), andhe = effective height for consideration of buckling in m.NOTE — Intermediate values may be linearly interpolated.

Ratiohe /D-----------------

IS 6533 (Part 2) : 1989

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Table 4 Temperature Coefficient, Kt

( Clause 7.8.1 )

7.12 Deflection Stresses

If the chimney carries a vertical load other thanits own weight, due for example, to the reactionof guys, lining or an imposed vertical load sothat an appreciable compressive stress results,deflection due to wind may cause the axial loadto become eccentric, the bending moment soproduced shall be determined, added to thatfrom the windload and any other live or deadload and used to calculate the combind stresswhich shall not exceed those specified in 7.8.This procedure is necessary only if the totalaxial load produces stresses greater thanone-third of the bending stress due to wind.7.13 Factor of Safety for Guy Ropes and Fittings

A minimum factor of safety of 3 shall beadopted in the design of guy ropes and otherfittings.7.13.1 For guyed chimney, it is necessary toestablish the safety of the chimney shell andguys for the forces induced due to temperatureeffect.7.14 Foundation

The foundation shall be designed for the worstcombination of loads specified in 6, such thatthe resulting pressure on the subsoil byconsidering the dead weight, movements andhorizontal forces, is limited to safe bearingcapacity of the soil. Necessary care should betaken on the effects of the temperature andseasonal changes.8 DESIGN CALCULATION8.1 General

Design of chimney shall be such that thestresses in any part of the chimney do notexceed the values specified in 7 for the loadsand load combinations given in 6.8.2 Calculation of Static Wind Load

8.2.1 Static wind pressure, q, acting normal tothe surface of chimney shall be taken asspecified in IS 875 (Part 3) : 1987 for theappropriate wind zone, terrain and topography.8.2.2 To determine the wind force acting atdifferent heights of chimney, the latter shall bedivided into a number of convenient zones suchthat the number of zones shall not be less thanthree and the zone height shall not exceed 10 m.

8.2.3 Static wind force acting at the midpoint ofKth zone ( K varying from 1 to r ) shall becalculated from the formula,

Pst, k = C qk hk dkwhere Pst, k = static wind load acting at the

midpoint of Kth zone, in N;qk = static wind pressure at the

midpoint of Kth zone, in Pa;hk = height of Kth zone strip, in

metres;dk = external diameter of chimney of

Kth zone, in metres taking intoaccount strakes, if fitted. Forchimney with strakes, this shallbe 1.2 times the externaldiameter of the chimney shell;and

C = shape factor for chimney whichmay be taken as 0.7 for theportion with circular crosssection, without strakes.

NOTE — For other shapes, surface conditions,attachments, line platform, hand rails and for groups ofchimneys on suitable shape factors shall be taken.

8.3 Calculation of Dynamic Wind Loads

8.3.1 In case of self-supported chimneys, if theperiod of natural oscillation for the chimneycomputed as given below exceeds 0.25 seconds,the design wind loads shall take intoconsideration the dynamic effect due topulsation of thrust caused by wind velocity inaddition to the static wind load calculatedunder 8.2.3.The natural frequency, first mode, for achimney of varying diameter or thickness, shallbe calculated by dividing the chimney into anumber of convenient zones as given in 8.2.2.

The frequency f =

wherem = mass of the zone including the lining or

covering, in kg;x = deflection of the same zone due to the

force equal to gravity acting on its massnormally at the mass centre with thebase fixed and top free, in metres; and

g = rate of gravitational acceleration= 9.8 m/s2.

8.3.2 Dynamic effect of wind is influenced by anumber of factors, such as, mass and itsdisposition along chimney height, period andmode of natural oscillation. 1ogarithmicdecrement of dampening, pulsation of velocitythrust, etc. Values of dynamic components ofwind load should be determined for each modeof oscillation of the chimney as a system ofinertia forces acting at the centre of the zonebeing considered.

Temperature, °C

0-200 250 300 350 400K t 1.0 0.75 0.67 0.6 0.5

NOTE — Intermediate values shall be linearlyinterpolated.

IS 6533 (Part 2) : 1989

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Inertia force Pdyn, in N acting at the centre ofthe jth zone of the chimney in the ith mode ofnatural oscillation is determined as follows ( seeFig. 1 ):

Pdyn, ij = Mj ξi ηij

where

Mj = mass of the jth zone in kgconcentrated at its centre,

ξi = dynamic coefficient in accordancewith 8.3.3,

ηij = deduced acceleration in m/s2 of thecentre of the jth zone taken inaccordance with 8.3.4, and

= coefficient which takes care of thespace correlation of wind pulsationspeed according to height andvicinity of building structures and istaken in accordance with 8.3.5.

8.3.3 Dynamic coefficient ξi (for lined andunlined chimney) is determined from Table 5depending on the parameter ξi :

ξi =

Ti = period of ith mode of natural oscillationin seconds, and

Vb = basic wind speed in m/s.

Table 5 Coefficient of Dynamic Influence ξi for Steel Chimneys

( Clause 8.3.3 )

8.3.4 Deduced acceleration ηij, in m/s2 isdetermined according to formula:

whereMk = mass of the kth zone, in kg;

ij, ik = relative ordinates of mode shapecorresponding to the centres of jthand kth zones in the ith mode ofoscillation. In special casesinvolving the interaction of soilstructure affecting the modeshape considerably, the relativeordinates shall be accordinglycalculated.;

Pst,k = wind load on the kth zonedetermined according to 8.2.3;

r = number of zones into which thechimney is divided; and;

mk = coefficient of pulsation of speedthrust for the centre of the kthzone, taken as in Table 6.

8.3.5 The value of coefficient shall be takenfrom Table 7 depending upon the parameter ξias given in 8.3.4. For structures of cantilevertype, v shall be taken only for the first mode ofnatural oscillation. For higher modes, shallbe taken as 1.8.3.6 While determining the wind load on thechimney, consideration of the first mode ofnatural oscillation is sufficient. It isrecommended to consider higher modes ofoscillation only when the chimney is very tall, say,80 and above and when consideration of mass,stiffness and disposition of various loads actingon the chimney require a more thorough analysis.

FIG. 1 DESIGN SCHEME OF CHIMNEY IN THE ith MODE OF OSCILLATION

Ti Vb1 200---------------

ξi Values of ξi for

LinedChimney

UnlinedChimney

00.0250.0500.0750.1000.1250.1500.1750.200

1.201.701.902.102.302.452.602.702.75

1.302.503.103.503.754.104.304.504.70

NOTE — Intermediate values may be linearlyinterpolated

IS 6533 (Part 2) : 1989

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Table 6 Coefficient of Pulsation of Speed Thruts, mk

( Clause 8.3.4 )

Table 7 Coefficient ( Clause 8.3.5 )

8.3.7 Total design lateral force ( Pk ), bendingmoment ( Mk ) and deflection ( k ) due to windload should be computed from static anddynamic calculations corresponding to the ithmode of natural oscillation and summed upaccording to the following formulae:

where

Pst,k and Pdyn,k = the static and dynamicwind load acting at midpoint of kth zone,respectively;

Mst,k and Mdyn,k = bending moments due tothe static and dynamicwind pressurerespectively, acting atkth zone;

stk and dyn,k = deflections due to staticand dynamic windpressure respectively atthe kth zone withrespect to the originalposition; and

s = number of modes ofoscillation.

8.4 Check for Resonance

8.4.1 In case of self-supporting chimney,checking for resonance shall be carried out ifthe critical velocity Vcr as determined fromAnnex A is within the range:

a) 0.5 to 0.8 times the design wind velocityfor lined chimneys, and

b) 0.33 to 0.8 times the design wind velocityfor the unlined chimneys.

8.4.2 For lined chimneys, checking forresonance should be carried out for both thecases, that is, with and without lining.8.4.3 Design force F, bending moment M anddeflection at level z during resonance shall bedetermined by formulae:

whereFres,z, Mres,z and res,z = transverse force,

bending momentand deflection atresonance respec-tively at level z( see A-5 );

Fst,z, Mst,z and st,z = static transverseforce, bendingmoment anddeflection due tostatic wind load( see A-6 ); and

Fdyn,z, Mdyn,z and dyn,z = dynamic transverse force, bendingmoment anddeflection due todynamic wind load( see 8.3.2 ).

8.5 Holding Down Bolts

The maximum stress in holding down boltscalculated taking into account the worstcombination of loading shall not exceed thepermissible stresses as specified in IS 800 :1984.

Type of Location

Height Above Ground Level, in m

Up to 10

20 40 60 100 200 350 andabove

A 0.60 0.55 0.48 0.46 0.42 0.38 0.35

B 0.83 0.75 0.65 0.60 0.54 0.46 0.40

NOTES1 Type A relates to open locations (Steppe, desert, seacoast, lake, reservoir, etc).2 Type B relates to outskirts of town, widespread forestand its like, regular obstacles of height more than 10 m.

Height of Chimney, in m

ξi

Up to 45

60 120 150 300 450 and above

≤ 0.050.10.2

0.70——

0.650.75—

0.600.650.75

0.550.600.70

0.450.500.60

—0.400.50

NOTE — Intermediate values may be linearly inter-polated.

IS 6533 (Part 2) : 1989

10

8.6 Design of Base PlateThe maximum stresses in the base plate andstiffeners and bearing pressure on foundationshall be calculated for the worst combination ofloading and shall not exceed the permissiblevalues in accordance with the relevantprovisions of IS 800 : 1984 and IS 456 : 1978.

9 STABILITY

9.1 Structure9.1.1 The stability of the structure as a whole orany part of it shall be investigated andcalculations shall be made to show that thestresses imposed by 1.6 times the total of windload plus any stress increasing imposed loads,less 0 9 times the minimum dead load excludingany stress reducing imposed loads, will notexceed 1.8 times the allowable stress specified.

1.6 ( σw + σm ) — 0 9 σe < 1.8 σa

where

σw = stress produced by wind load,σm = stress produced by any other load

which may act to increase thecombined stress,

σe = stress produced by dead load and anyother load which acts at all times andwill reduce the combined stress, and

σa = maximum permissible stresses at theoperating temperature.

9.1.2 To ensure stability at all times, accountshall be taken of probable variations in deadload during construction, repair or othersimilar work.9.1.3 While computing the stability, it shall beensured that the resulting pressure and shearforces to be transferred to the supporting soilthrough foundation, will not cause failure offoundation.

9.2 Structure and Foundations

9.2.1 In the case of guyed or laterally supportedchimneys, the stability of the structure andfoundation as a whole or any part of it shall beinvestigated and weight or anchorage shall beprovided so that, without exceeding theallowable material stresses and foundationbearing pressure, 0.9 times the least restoringmoment including anchorage will not be lessthan the sum of 1.1 times the maximumoverturning moment due to stress-increasingdead loads, less 0.9 times that due tostress-reducing loads, plus 1.4 times that due towind and imposed loads, that is

1.4 Mw + 1.1 Mm — 0.9 Me < 0.9 Ma

where

Mw = overturning moment produced by thewind and imposed loads,

Mm = overturning moment produced by deador other loads which may act toincrease combined moment,

Me = overturning moment produced by deador other loads which act at all times toreduce combined moment, and

Ma = resisting moment produced by thefoundation without exceeding theallowable material stress and theground stress without exceeding thefoundation bearing pressure.

9.2.2 In the case of self-supporting chimney,the stability of the structure as a whole shall beinvestigated and weight or anchorages shall beso proportioned that the least resisting momentshall be not less than the sum of 1.5 times themaximum overturning moment due to deadload and wind load/earthquake load.

10 MISCELLANEOUS COMPONENTS10.1 Base Plate and Holding Down BoltsHolding down bolts shall be adequatelytightened with appropriate precautions usingwashers and locknuts to prevent the strippingof threads and the base plate shall be properlygrouted. Typical details of base plate andholding down bolts are shown in Fig. 2.10.2 Base Gussets and StoolsWhere base gussets or stools are used, theyshould preferably be evenly disposed aroundthe chimney shell. Smaller secondary gussetsmay be provided between the main gussets.Base gussets shall be of ample height and shallextend to the edge of the base plate. The angleof the sloping edge of any gusset to thehorizontal shall be not less than 60°. Theminimum thickness of the gusset shall be8 mm.10.3 Chimney HeadThe chimney head shall be strengthened in asuitable manner on the basis of the design andshall have provisions for the attachment oferection and maintenance equipment.10.4 Galleries and PlatformsGalleries and platforms for erection and serviceof warning lamps, earthing, inspection, etc,should be provided around the chimneywherever necessary. Their width shall be atleast 800 mm. These shall be provided withhandrails of height, Im. The number andlocation of galleries and platforms may bemutually decided between the designer and thecustomer.10.5 Inspection/Cleaning DoorSuitable door for access near the base, to theinside of the chimney shall be provided for thepurpose of inspection of the inside of thechimney and also for ash removal. Theminimum size of the door opening shall be500 mm wide × 800 mm high clear ( see Fig. 3 )

IS 6533 (Part 2) : 1989

11

FIG. 2 TYPICAL DETAILS OF BASE OF STEEL CHIMNEY

FIG. 3 TYPICAL DETAILS OF CHIMNEY DOOR AND BOILER DUCTS

IS 6533 (Part 2) : 1989

12

10.6 Protection Against Lightning

The chimney shall be provided with lightningprotection arrangements in accordance withIS 2309 : 1963.

10.7 Warning Lamps

Suitable warning lamps shall be provided. Therecommended number and position of the same,depending upon the height of the chimney is givenin Fig. 4. Whenever only one warning lamp isshown in the figure, 2 numbers of lamps have tobe provided diametrically opposite to each other.10.7.1 Existing local and aviation regulations,if any, should be followed ( see 3.1 also ).

10.8 Baffle Plates

When there are two or more breach openings orflues entering the chimney, baffle plates shallbe provided to properly direct the gases fromflue duct up the chimney and prevent themfrom interfering with the operation of the otherflue. These baffles shall be properly insulated.

10.9 Rigging Screws (Turn Buckles)

Rigging screws shall conform to IS 3121 : 1965.These shall be provided with lock nuts toprevent slacking back.

10.10 Steps and Ladders

10.10.1 Steps

10.10.1.1 Typical connection details of steps tochimney shell are shown in Fig. 5.

10.10.1.2 The steps shall be welded to theoutside of the chimney at a spacing of 300 mm.In the case of shafts of clear diameter of3 000 mm and more, a second row of steps shallbe welded on the diametrically opposite side.Proper anticorrosive measure or alternatively,proper selection of material for the steps shallbe adopted keeping in view the location in thechimney and the extent of corrosion involved.

Position ofLamp

Height of Lamp in m for Chimney Height h

a

b

c

32.0030.50

——

56.0054.4027.00

—

63.0061.0031.50

—

70.0068.5033.50

—

80.0078.5098.50

—

90.0068.5043.50

—

100.0098.5048.50

—

110.00108.00

73.5038.50

All dimensions in millimetres.

FIG. 4 LOCATION OF WARNING LAMPS OF THE CHIMNEY

IS 6533 (Part 2) : 1989

13

10.10.1.3 On the inner side of the chimney,steps may be welded at a spacing of 300 mm. Ifthe steps are to be directly supported on thelining, the lining should have a minimumthickness of 200 mm. Where the lining isthinner than the above, the steps shall bewelded direct to the shell with adequateclearance when the lining does not expandalong with the shell. In case where thediameter does not permit providing stepsinside, painter’s trolley should be used forapproach.

10.10.2 LaddersTypical connection details of ladders are shownin Fig. 6.

10.10.2.1 Steel ladders may also be provided inaddition to steps. Safety enclosure or cage shallbe provided for chimneys taller than 20 mstarting from a height of 3 m from ground.10.10.2.2 If individual section of a ladderexceeds 20 m in height, an intermediatelanding platform shall be provided.10.11 Position of Guys

10.11.1 Guys shall be positioned sufficientlybelow the outlet of the chimney to avoid thecorrosive action of the emergent combustionproducts. A minimum distance of 3 m isrecommended. There shall be a minimum ofthree guy ropes to each set, guys shall bepositioned radially in plan and the anglebetween any adjacent pair of guys shall notexceed 130°. The guy ropes shall not exceed anangle of 60° to the horizontal.

11 CONSTRUCTION

11.1 General

The fabrication and erection of steel chimneys,guys, etc, shall generally be in accordance withIS 800 : 1984. For welded chimneys, weldingshall be carried out in accordance withIS 816 : 1969 and IS 9595 : 1980.11.1.1 Non-destructive testing of weld, ifrequired, may be carried out as mutuallyagreed between the parties concerned.11.2 Erection Tolerance

The variation in the eccentricity of the axis ofchimney from the vertical at any level shall notexceed 1/1 000 of the height, at that particularsection.11.3 Clearance

Where a chimney passes through a roof or otherpart of a building, provision shall be made toaccommodate the movement of the chimney and

FIG. 5 STEPS FOR STEEL CHIMNEYS

FIG. 6 TYPICAL CONNECTION DETAILS FOR LADDER

IS 6533 (Part 2) : 1989

14

to limit the transfer of heat. Normally, an air gapof 50 mm is desirable. Flexible heat resistantpacking may be used to fill the gap, if necessary.11.4 Sealing

Riveted chimneys shall be caulked, specially ifcondensation is likely to occur.11.5 Gas Tightness

No gaskets shall be used in jointing flanges onstructural steels.

NOTE — Liquid sealants are recommended to ensuregas tightness and prevent corrosion in the meeting faces.

10.6 Erection Tension

The amount of pretensioning applied to the guyropes on site shall be in accordance with theappropriate design considerations and may bemeasured with a suitable instrument. Thetension in the guys after erection shall be notless than 15 percent nor more than 30 percentof the calculated maximum tension due towind.12 INSPECTION AND MAINTENANCE12.1 All steel chimneys shall be inspected andexamined at least once a year.12.1.1 In case of uninsulated and unlined steelchimneys, the thickness of the shell should bedetermined by either ultra-sonic thicknesstesting or by drill testing. At the same time,any decorative or other surface finish on theexterior of the chimney may be examined. Theinternal surface of large diameter steelchimneys may also be inspected preferably byclose examination from a painter’s trolley orsimilar means of support.12.1.2 Lined chimneys should also be inspectedinternally by close examination from a painter’strolley or similar means of support to ascertainthat the lining is still in serviceable conditionand fulfilling its task.12.2 The details of the painter’s trolley aregiven in Fig. 7 for information. For chimney ofdiameter exceeding 3 m at the top, two suchpainter’s trolleys should be provided.12.3 Flanges should be inspected to see if thereis a build-up of rust between them as thepressure of rust build-up can overload thebolts/rivets in tension. In bolted connections,particular attention should be given to theconditions of the bolts. Selected bolts in criticalareas should be removed, inspected, tested asnecessary and be replaced with the new bolts.Should the examined bolts be serviceable, theseshall not be reused.12.4 The rivet heads on the interior of rivetedchimney should be examined to ascertain thatthey are secure and have not eroded to adangerous degree.

12.5 Where loose fill is used for insulation, thisshould be inspected at three monthly intervalsin the first 12 months and then annually. Theloose fill should be checked to ensure that it hasnot compacted and, if necessary, it should betopped up.

12.6 Detailed record should be submitted aftereach inspection describing any recommendedmaintenance.

12.7 Guy wire and fittings, where present,should be examined for security tension and, ifnecessary, be cleaned and greased.

13 PROTECTIVE TREATMENTS

13.1 Surface Preparation for Painting

Consideration should be given to the surfacepreparation and protective treatment of boththe exterior and interior surfaces of chimneyshells in order to prolong the life and improvethe appearance of the chimney. Immediatelybefore applying any protective treatment to theexterior or the interior surface of a steelchimney shell, the surface shall be cleaned bychipping, scrapping and wire brushing, or byother means to remove all dirt, loose scale,grease, rust or other deleterious materials.13.1.1 Pretreatment and painting of chimneyshell parts shall generally conform to therequirements of IS 1477 (Part 1) : 1971 andIS 1477 (Part 2) : 1971.

13.2 Painting of Interior Surfaces

13.2.1 Unlined Chimney ShellThere is generally no advantage in applying aprotective treatment except for the applicationof one coat of suitable priming paint to theinterior surface of an unlined chimney shellunless it can be shown that such treatment willwithstand the corrosive, abrasive and thermaleffects of the flue gases and thus prolong thelife of the chimney.

13.2.2 Lined Chimney ShellWhen it is thought desirable to use a protectivetreatment on the interior steel surface of alined chimney, such treatment shall consist ofthe application of one coat of a suitable primingpaint followed by two coats of a finishing paintor paints applied in accordance with theinstructions of the manufacturer.

13.2.3 Multiflue Chimney Shells

The interior surface of the structural shell of amultiflue chimney shall be given one coat of asuitable paint, applied in accordance with theinstructions of the manufacturer.

IS 6533 (Part 2) : 1989

15

FIG. 7 TYPICAL DETAILS OF PAINTER’S TROLLEY ARRANGEMENT

IS 6533 (Part 2) : 1989

16

13.2.4 Chimney Shells with Monolithic LiningsThe interior steel surface of a chimney which isto be given a monolithic lining needs no furtherprotective treatment. The surface shall,however, be clean and dry immediately beforethe application of the lining.13.3 Painting of Exterior Surfaces

13.3.1 Exposed Steel SheetImmediately after the surface preparationoutlined in 13.1 has been completed, theexterior surface shall be given a coat of suitablepriming paint followed by one coat of finishingpaint applied in accordance with therecommendations of the manufacturer of theparticular paint. A final coat of paint shall beapplied after erection.Special attention should be paid to the upperportion of the exterior surface, that is, for adistance of 1 to 2 times the chimney diametersdown from the top where only those protectivetreatments should be applied which are bestable to withstand the corrosive action of theemerging flue gases.13.3.2 Shell with External CladdingShells with external cladding shall comply with13.3.1 except where the cladding or insulationis fitted at the works in which case the finalcoat of paint may be omitted.13.3.3 Multi-Flue Chimney FrameworkWhere a framework forms supporting structureof a multi-flue chimney, the treatmentdescribed in 13.3.1 shall be applied.13.4 Metal Spraying

13.4.1 GeneralThe exterior of a steel chimney may beprotected from atmospheric corrosion by theapplication of a sprayed metal coating.Aluminium is the preferred metal for thisapplication (certain other metals havedisadvantages when used for hot surfaces).The initial metal spray treatment shall beapplied under controlled conditions beforeerection and care shall be taken to avoiddamage during transportation and erection.Regions of damage where the coating has beenremoved over an area, the maximum width ofwhich exceeds 6 mm, shall be reblasted andresprayed, care being taken to avoid damagingor loosening the bond in contiguous areas.Minor areas of damage may be rectified by theapplication of a suitable aluminium paint aftercleaning.The finished appearance of sprayed chimneysmay not be uniform shading or texture.

13.4.2 SpecificationsSurface preparations and metal spraying shallbe done in accordance with the requirementsstipulated in IS 6586 : 1972. Recognizedpractices depending on the surface temperatureof shell may also be taken in account.13.4.3 Surface Preparation13.4.3.1 It is essential that the blast-cleanedsurface is sufficiently rough and clean toprovide an adequate key for the sprayedaluminium coating. The amplitude of the blastcleaned surface shall be (0.l ± 0.05) mm.13.4.3.2 Compressed air for nozzle blastcleaning shall be effectively free from oil andmoisture. The pressure during the blastingprocess shall be not less than 400 kPa at thenozzle.13.4.4 Methods of Application and Sealing ofCoatings13.4.4.1 For shell temperatures up to 200°C,the aluminium spray shall be applied by theelectric arc or flame spraying process.13.4.4.2 For shell temperatures exceeding200°C, the aluminium coating shall normallybe applied by the electric arc process. The flamespraying process may be used if the chimney isnot to be subjected to thermal shocksfrequently produced by gas turbine exhausts.The spray shall be sealed with a suitablesilicone based high temperature paint, appliedas a flood coat.13.4.4.3 The nominal thickness of the coatingshall be not less than 0.18 mm.13.4.4.4 Sealing coatsThe sprayed aluminium coating shall be sealed.For temperatures not exceeding 150°C, certainorganic base sealers or paints are suitable.Special high temperature resistant paints shallbe selected for use at temperatures exceeding150°C, that is, resin-modified silicone basepaints. Silicone base paints shall be usedaccording to the manufacturer’s instructions.13.4.4.5 Application of sealing coatsSealing coats shall be applied to clean drysurfaces. Any oil, grease or other contaminantsshall be removed by thoroughly washing withthinners until no visible traces ofcontamination exist and the surface shall beallowed to dry for at least 15 minutes beforeapplying the coating. Sealing coats shall beapplied heavily enough to produce a wetappearance and shall be applied in accordancewith the manufacturer’s instructions. Thetreatment shall be applied at the contractor’sworks as soon as practicable after spraying.

IS 6533 (Part 2) : 1989

17

ANNEX A( Foreword and Clauses 8.4.1 and 8.4.3 )

WIND EXCITED OSCILLATIONSA-1 GENERALChimneys are subject to oscillation due to windaction. This annex explains the procedures toinclude the effects of wind excited oscillationsas enumerated and suggests alternativeprocedures for making an appropriate increasein the design wind loading and indicates whenstrengthening or the incorporation of devicesfor suppressing von Karman type of oscillationsis advisable.A-1.1 It has been found that chimneys ofcircular cross section oscillate strongly acrosswind than along wind. It is, therefore,reasonable to continue with the currentpractice which implies that along wind, theoscillation will not cause stresses greater thanthose calculated for the wind velocities asspecified in IS 875 (Part 3) : 1987 due to staticloading along with dynamic coefficientproposed in this standard.A-1.2 Lateral oscillation due to resonanceeffects within the critical wind speed range atthe natural period of a cylindrical structuremay be great enough when its effect is addedvectorially to the down wind deflection, to causestresses higher than those calculated for theshort duration wind velocities in accordancewith this code due to static loading along withthe dynamic coefficient as specified in thisstandard.A-2 VON KARMAN VORTEX SHEDDINGThe regular fluctuating side force due tocommonly known as Von Karman vortexshedding, which may be produced in a smoothair flow, will produce strong oscillation at avelocity which gives resonance with the naturalfrequency of the structure. This effect isresisted by high damping and may beprevented by helical strakes or other devicesattached to a circular chimney. If the tendencyis strong, it is not effectively withstood byincrease of strength alone.A-2.1 In a natural wind, the regular vortexshedding may be interfered with by fluctuationof the wind so that the build-up of amplitude isnot continuous as in a wind tunnel, and it maybe more effectively resisted by mass andstiffness. There are different views as to howthe vortex shedding should be allowed for inpractice but it is clear that low damping, lowmass and large flexibility must increase theprobability and the amount of the oscillation ofchimneys. In many cases, the behaviour cannotbe predicted with certainty.A-2.2 Even in the worst cases, a chimney canbe made safe by applying guys or strakes at any

time after construction if experience showsthem to be required, and provided that thechimney is made strong enough in the firstplace to withstand the additional load fromguys or strakes applied later.For instance, helical strakes of three railshaving a projection of 0.1 to 0.12 times thediameter of the chimney, wound, equallyspaced, round the perimeter of the shell at apitch of about five times the diameter of thechimney for not less than the upperone-third of it.A-3 STROUHAL CRITICAL VELOCITYSevere Von Karman type oscillation is notlikely if the calculated velocity, known as ‘thecritical strouhal velocity’, is greater than themaximum design velocity based on IS 875(Part 3) : 1987. The strouhal critical velocity Vcrin m/s for a circular chimney may be calculatedfrom the formula:

wheref = natural frequency of the chimney

(in Hz) as obtained in 8.3.1, andDt = diameter of chimney at top (in m).NOTE — The formula for Vcr holds good for strouhalnumber of 0.2. This value remains fairly constant asshown by experiments.

A-4 AERODYNAMIC FORCEFor checking of resonance amplitude, theintensity of aerodynamic force Fi ( z ) at level z,for the ith mode of oscillation is determined bythe formula:

where

i ( z ) = relative ordinate at level z in theith mode oscillation;

Cyqcrdzhz = amplitude of force intensity at thefree end of the self-supportingchimney or at the centre of thespan of guyed chimney and is equalto Cy, qcr, dz, hz;

Cy = coefficient of transverse force takenequal to 0.25;

qcr = speed thrust corresponding tocritical velocity Vcr and is equal to

dz = diameter of the chimney at level zand z is in metres; and

hz = height of the zone at level z.

Vcr = 5 Dt × f . . . (1)

Fi ( z ) = Cyqcrdzhz i ( z ) . . . (2)

V cr2

16-----------;

IS 6533 (Part 2) : 1989

18

A-4.1 For self-supporting chimney (cantilevertype structures), only the first mode ofoscillation shall be considered.A-5 Inertia forces, amplitude of resonanceoscillations and dynamic bending moment at asection under consideration of a chimney fixedat foundation are determined by the followingformulae:

whereFres,z = intensity of inertia forces at

resonance at level z,

res,z = amplitude of resonance oscillationat level z,

Μres,z = bending moment at resonance atlevel z,

Fst,z = intensity of lateral static force atlevel z,

st,z = static deflection at level z (sectionunder consideration) under theaction of static force,

Μst,z = bending moment at level z (sectionunder consideration) due to theaction of static force,

= logarithmic decrement of dampen-ing effect to be taken equal to:a) 0.1 for steel chimney with

lining, andb) 0.05 for unlined steel chimneys.

A-6 Static wind-load qcr (stat) in the directionof action of wind corresponding to criticalpressure qcr is permitted to be taken asconstant along the height of the chimney and is

calculated from the height of the chimney andis calculated from the formula:

qcr (stat) = C qcr

whereC = shape factor in accordance with 8.2.3.

A-7 The corresponding dynamic wind load qcr(dyn) shall be determined in accordance with8.3.2 to 8.3.7 corresponding to qcr.A-8 Checking for resonance is not required forother short duration forces. The provisions forchecking resonance will not necessarily applyto pairs, files and groups of chimneys or othertall structure which may oscillate excessivelyparticularly if they are closer thanapproximately 12 diameters. The fitting ofstabilizers is usually beneficial but may notalways be effective. No simple rules can besuggested. Study of the layout by specialistsand wind tunnel testing may be necessary.A-9 Chimneys which have a highdiameter/thickness ratio may be subjected towind-generated ovalling oscillation due tocircumferentially varying and fluctuatingpressure. Besides causing circumferentialbending stresses, this can increase verticalstresses in the lower part of a chimney of largediameter. It should be avoided by providingsufficient circumferential stiffness aroundchimney at the top. Chimneys having grossplate thickness of less than 1/300 of thediameter if not efficiently stiffened by a liningor encasing, should have stiffened rings addedat the top (and lower down if the height is morethan 20 times the diameter). The distancebetween the stiffening rings should be not morethan 1 500 times the thickness of the shell andshould be substantial enough to give a totalcircumferential bending stiffness at leastequvalent to that of a uniform shell of thickness

of the diameter.

ANNEX B( Clause 2.1 )

LIST OF REFERRED INDIAN STANDARDS

Fres,z = Fst,z . . . (3)

res,z = st,z . . . (4)

Μres,z = Μst,z . . . (5)

πδ---

πδ---

πδ---

1200----------

IS.No. Title

226 : 1975 Structural steel (standardquality) ( fifth revision )

456 : 1978 Code of practice for plain andreinforced concrete ( thirdrevision )

800 : 1984 Code of practice for generalconstruction in steel ( secondrevision )

IS.No. Title

814 Covered electrodes for metalarc welding of structural steel:

(Part 1) : 1974 For welding products otherthan sheets ( fourth revision )

(Part 2) : 1974 For welding sheets ( fourthrevision )

IS 6533 (Part 2) : 1989

19

IS.No. Title816 : 1969 Code of practice for use of metal

arc welding for generalconstruction in mild steel ( firstrevision )

875 Code of practice for designloads (other than earthquake)for building structures:

(Part 1) : 1987 Dead loads — Unit weights ofbuilding materials and storedmaterials ( second revision )

(Part 3) : 1987 Wind loads ( second revision )961 : 1975 Structural steel (high tensile)

( second revision )1030: 1982 Carbon steel castings for

general engineering purposes( third revision )

1149 : 1982 High tensile steel rivet bars forstructural purposes ( thirdrevision )

1363 : 1984 Hexagon head bolts, screwsand nuts of product grade C

1364 : 1983 Hexagon head bolts, screwsand nuts of product grades Aand B

1367 Technical supply conditions forthreaded steel fasteners:

(Part 1) : 1980 Introduction and generalinformation ( second revision )

(Part 3) : 1979 Mechanical properties and testmethods for bolts, screws andstuds with full loadability( second revision )

(Part 6) : 1980 Mechanical properties and testmethods for nuts with specifiedproof loads ( second revision )

1395 : 1982 Low and medium alloy steelcovered electrodes for manualmetal arc welding ( thirdrevision )

1477 Code of practice for painting offerrous metals in buildings:

(Part 1) : 1971 Pretreatment ( first revision )(Part 2) : 1971 Painting ( first revision )

1893 : 1975 Criteria for earthquakeresistant design of structures( fourth revision )

1929 : 1982 Hot forged steel rivets for hotclosing ( 12 to 36 mm )diameter ( first revision )

2062 : 1984 Weldable structural steel( third revision )

IS.No. Title2141 : 1979 Galvanized stay strand ( second

revision )2155 : 1982 Cold forged solid steel rivets for

hot closing (6 to 16 mmdiameter) ( first revision )

2266 : 1970 Steel wire ropes for generalengineering purposes ( secondrevision )

2309 : 1963 Code of practice for theprotection of buildings and alliedstructures against lightning( first revision )

3613 : 1974 Acceptance tests for wire-fluxcombinations for submerged arcwelding of structural steels( first revision )

3640 : 1982 Hexagon fit bolts ( first revision )3757 . 1972 High strength structural bolts

( second revision )5369 : 1975 General requirements for plain

washers and lock washers ( firstrevision )

5370 : 1969 Plain washers with outsidediameter 3 × inside diameter

5624 : 1970 Foundation bolts6419 : 1971 Welding rods and bare

electrodes for gas shielded arcwelding of structural steel

6560 : 1972 Molybdenum and chromium-molybdenum low alloy steelwelding rods and base electrodesfor gas shielded arc welding

6586 : 1972 Recommended practice for metalspraying for protection of ironand steel

6610 : 1972 Heavy washers for steelstructures

6623 : 1972 High strength structural nuts( first revision )

6639 : 1972 Hexagon bolts for steelstructures

6649 : 1972 Hardened and temperedwashers for high strengthstructural bolts and nuts ( firstrevision )

7002 : 1972 Prevailing torque type steelhexagon locknuts

7280 : 1974 Bare wire electrodes forsubmerged arc welding ofstructural steels

8500 : 1977 Weldable structural steel(medium and high strengthqualities)

IS 6533 (Part 2) : 1989

20

ANNEX C( Clause 7.7.2 )

ALLOWABLE COMPRESSIVE STRESSES

C-1 COMPRESSIVE STRESSES IN THE SHELL

C-1.1 To control buckling, the compressivestresses caused by the combination of extremefibre stress due to buckling and direct load, asgiven in Table 3, are worked out by theformula:

0 5 fy A·Bwhere

fy = yield stress of steel; 250 MPa for steelof IS 226 and 2062;

A =

and

A =

and B =

and

B =

t = thickness of plate at the levelconsidered, in m;

D = mean diameter at the level considered,in m; and

he = effective height for the consideration ofbuckling, in m ( see Table 2 ).

1

0.84 + 0.019 heD

-------- 2

-----------------------------------------------------------, if heD------ > 21

1 if heD------ < 21

270 tD---- 1–67 t

D----

, if Dt---- > 130

1, if Dt---- < 130

Bureau of Indian Standards

BIS is a statutory institution established under the Bureau of Indian Standards Act, 1986 to promoteharmonious development of the activities of standardization, marking and quality certification of goods andattending to connected matters in the country.

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BIS has the copyright of all its publications. No part of these 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 Standards

Amendments are issued to standards as the need arises on the basis of comments. Standards are alsoreviewed periodically; a standard along with amendments is reaffirmed when such review indicates that nochanges are needed; if the review indicates that changes are needed, it is taken up for revision. Users ofIndian Standards should ascertain that they are in possession of the latest amendments or edition byreferring to the latest issue of ‘BIS Catalogue’ and ‘Standards : Monthly Additions’.

This Indian Standard has been developed from Doc : No. CED 7 (4721)

Amendments Issued Since Publication

Amend No. Date of Issue

Amd. No. 1 June 1998

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