gov.bd.bnbc

Part6 StructuralDesign 6365

Chapter 7

MASONRYSTRUCTURES

7.1 INTRODUCTION

7.1.1 ScopeThischapteroftheCodecoversthedesign,constructionandqualitycontrolofmasonrystructures.

7.1.2 SymbolsandNotationThefollowingunitsshallbegenerallyimplicitinthischapterforthecorrespondingquantities: Lengths mm Areas mm2 Momentofinertia mm4 Force N Moment,torsion Nmm Stress,strength N/mm2

a = depthofequivalentrectangularstressblockforstrengthdesign Ab = crosssectionalareaofanchorbolt Ae = effectiveareaofmasonry Ag = grossareaofwall Amv= netareaofmasonrysectionboundedbywallthicknessandlengthofsectioninthedirectionof

shearforceconsidered Ap = area of tension (pullout) cone of an embedded anchor bolt projected into the surface ofmasonry As = effectivecrosssectionalareaofreinforcementinaflexuralmember Av = areaofsteelrequiredforshearreinforcementperpendiculartothelongitudinalreinforcement

sA = effectivecrosssectionalareaofcompressionreinforcementinaflexuralmember b = effectivewidthofrectangularmemberorwidthofflangeforTandIsection bt = computedtensionforceonanchorbolt bv = allowableshearforceonanchorbolt bw = widthofwebinTandImember Bt = allowabletensionforceonanchorbolt Bv = computedshearforceonanchorbolt c = distancefromtheneutralaxistoextremefibre Cd = masonryshearstrengthcoefficient d = distancefromthecompressionfaceofaflexuralmembertothecentroidoflongitudinaltensile

reinforcement db = diameterofthereinforcingbar,diameterofbolt

e = eccentricityofPu emu= maximumusablecompressivestrainofmasonry

Part6StructuralDesign

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Em = modulusofelasticityofmasonry Es = modulusofelasticityofsteel fa = computedaxialcompressivestressduetodesignaxialload fb = computedflexuralstressintheextremefibreduetodesignbendingloadonly fmd = computedcompressivestressinmasonryduetodeadloadonly fr = modulusofrupture fs = computedstressinreinforcementduetodesignload fy = tensileyieldstressofreinforcement fv = computedshearstressduetodesignload

f m = specifiedcompressivestrengthofmasonryattheageof28days F = loadsduetoweightandpressureoffluidsorrelatedmomentsandforces Fa = allowableaverageaxialcompressivestressforcentroidallyappliedaxialloadonly Fb = allowableflexuralcompressivestressifmemberswerecarryingbendingloadonly Fbr = allowablebearingstress Fs = allowablestressinreinforcement Fsc = allowablecompressivestressincolumnreinforcement Ft = allowableflexuraltensilestressinmasonry Fv = allowableshearstressinmasonry G = shearmodulusofmasonry h = heightofwallbetweenpointsofsupport h = effectiveheightofawallorcolumn H = actualheightbetweenlateralsupports H' = heightofopening I = momentofinertiaabouttheneutralaxisofthecrosssectionalarea Ig,Icr= gross,crackedmomentofinertiaofthewallcrosssection j = ratioordistancebetweencentroidofflexuralcompressiveforceandcentroidoftensileforcesto

depth,d k = ratioofdepthofthecompressionzoneinflexuralmembertodepth,d;stiffeningcoefficient l = lengthofawallorsegment lb = embedmentdepthofanchorbolt lbe = anchorboltedgedistance,theleastlengthmeasuredfromtheedgeofmasonrytothesurfaceof

theanchorbolt ld = requireddevelopmentlengthofreinforcement L = actuallengthofwall M = designmoment Mc = moment capacity of the compression steel in a flexuralmember about the centroid of thetensile

force Mcr= crackingmomentstrengthofthemasonrywall Mm= themomentofthecompressiveforceinthemasonryaboutthecentroidofthetensileforcein

thereinforcement Mn = nominalmomentstrengthofthemasonrywall

MasonryStructures Chapter7

BangladeshNationalBuildingCode2012 6367

Ms = themomentofthetensileforceinthereinforcementaboutthecentroidofthecompressive

forceinthemasonry Mser = servicemomentatthemidheightofthepanel,includingPDeltaeffects Mu = factoredmoment n = modularratio=Es/Em P = designaxialload Pa = allowablecentroidalaxialloadforreinforcedmasonrycolumns Pb = nominalbalanceddesignaxialstrength Pf = loadfromtributaryfloororroofarea Po = nominalaxialloadstrengthwithbending Pu = factoredaxialload Puf = factoredloadfromtributaryfloororroofloads Puw = factoredweightofthewalltributarytothesectionunderconsideration Pw = weightofthewalltributarytothesectionunderconsideration

rb = ratiooftheareaofbarscutofftothetotalareaofbarsatthesection

s = spacingofstirrupsorbentbarsinadirectionparalleltothatofthemainreinforcement S = sectionmodulus t = effectivethicknessofawythe,wallorcolumn u = bondstressperunitofsurfaceareaofbar V = totaldesignshearforce Vn = nominalshearstrength Vm = nominalshearstrengthprovidedbymasonry Vs = nominalshearstrengthprovidedbyshearreinforcement u = horizontaldeflectionatmidheightunderfactoredload;PDeltaeffectsshallbeincludedin

deflectioncalculation

= steelratio=As/bd n = ratioofdistributedshearreinforcementonaplaneperpendiculartotheplaneofAmv o = sumoftheperimetersofallthelongitudinalreinforcement

= strengthreductionfactor.

7.1.3 DefinitionsForthepurposeofthischapter,thefollowingdefinitionsshallbeapplicable.

BEDBLOCK :Ablockbeddedonawall,columnorpiertodisperseaconcentrated loadonamasonryelement.BEDJOINT:Ahorizontalmortarjointuponwhichmasonryunitsareplaced. BOND : Arrangement of masonry units in successive courses to tie the masonry together bothlongitudinallyandtransversely;thearrangementisusuallyworkedouttoensurethatnoverticaljointofonecourseisexactlyovertheoneinthenextcourseaboveorbelowitandthereismaximumpossibleamountoflap.BONDBEAM:Ahorizontalgroutedelementwithinmasonryinwhichreinforcementisembedded. BUTTRESS : A pier ofmasonry built as an integral part ofwall and projecting from either or bothsurfaces,decreasing in crosssectional area frombase to top and conforming to the requirementofSec4.3.3(c)(ii).CAVITYWALL:Awallcomprisingtwolimbseachbuiltupassingleormultiwytheunitsandseparatedbya50115mmwidecavity.The limbsaretiedtogetherbymetaltiesorbondingunitsforstructuralintegrity.


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CELL:Avoidspacehavingagrosscrosssectionalareagreaterthan1000mm2.COLUMN:Anisolatedverticalloadbearingmemberthewidthofwhichdoesnotexceedthreetimesthethickness.CROSSJOINT:Averticaljointnormaltothefaceofthewall.CROSSSECTIONAL AREA OFMASONRY UNIT:Net crosssectional area ofmasonry unit is the grosscrosssectionalareaminustheareaofcellularspace.CURTAINWALL:Anonloadbearingselfsupportingwallsubjecttotransverselateralloads,andlaterallysupportedbyverticalorhorizontalstructuralmemberwherenecessary.DIMENSIONS:Actualdimensionsthemeasureddimensionsofadesignateditem;suchasadesignatedmasonryunitorwallused in the structures.The actualdimension shallnot vary from the specifieddimensionbymorethantheamountallowedintheappropriatestandardmentionedinSec2.2.4ofPart5.Nominaldimensions;specifieddimensionsplusthethicknessofthejointwithwhichtheunitislaid.Specified dimensions the dimensions specified for the manufacture or construction of masonry,masonryunits,jointsoranyothercomponentsofastructure.Unlessotherwisestated,allcalculationsshallbemadeusingorbasedonspecifieddimensions.FACEDWALL:Awall inwhich facing andbackingof twodifferentmaterials arebonded together toensurecommonactionunderload.GROUT :Amixtureof cementitiousmaterials and aggregate towhichwater is added such that themixturewillflowwithoutsegregationoftheconstituents.GROUTEDMASONRY:Groutedhollowunitmasonrythatformofgroutedmasonryconstructioninwhichcertaindesignatedcellsofhollowunitsarecontinuouslyfilledwithgrout.Groutedmultiwythemasonrythatformofgroutedmasonryconstructioninwhichthespacebetweenthewythesissolidlyorperiodicallyfilledwithgrout.HOLLOWUNIT:Amasonryunitofwhichnetcrosssectionalarea inanyplaneparallel to thebearingsurfaceislessthan75percentofitsgrosscrosssectionalareameasuredinthesameplane.JAMB:Sideofanopeninginwall.JOINTS:Bedjoints;themortarjointthatishorizontalatthetimethemasonryunitsareplaced.Collarjoint;thevertical,longitudinal,mortarorgroutedjoints.Headjoint;themortarjointhavingaverticaltransverseplane.LATERALSUPPORT:Asupportwhichenablesamasonryelementtoresistlateralloadand/orrestrainslateraldeflectionofamasonryelementatthepointofsupport.LIMB:Innerorouterportionofacavitywall.LOADBEARINGWALL:Awalldesignedtocarryanimposedverticalloadinadditiontoitsownweight,togetherwithanylateralload.MASONRY:Anassemblageofmasonryunitsproperlybondedtogetherwithmortar.MASONRY UNIT : Individual units, such as brick, tile, stone or concrete block, which are bondedtogetherwithmortartoformamasonryelementsuchaswalls,columns,piers,buttress,etc.PANELWALL :Anexteriornon loadbearingwall in framed structure, supportedateach storeybutsubjecttolateralloads.PARTITIONWALL:Aninteriornonloadbearingwall,onestoreyorpartstoreyinheight.PIER : A projection from either or both sides of a wall forming an integral part of the wall andconformingtotherequirementofSec4.4.3.3.c(ii).PILASTER :A thickened section forming integralpartof awallplaced at intervals along thewall, toincrease the stiffnessof thewallor to carry a vertical concentrated load. Thicknessof apier is theoverall thickness including the thicknessof thewallor,whenbounded intoa limbofcavitywall, thethicknessobtainedbytreatingthatlimbasanindependentwall.



PRISM : An assemblage ofmasonry units bonded bymortarwith orwithout grout used as a testspecimenfordeterminingpropertiesofmasonry.REINFORCEDMASONRY:Themasonryconstruction,inwhichreinforcementactinginconjunctionwiththemasonryisusedtoresistforcesandisdesignedinaccordancewithSec4.6.SHEARWALL :A loadbearingwalldesigned tocarryhorizontal forcesacting in itsownplanewithorwithoutverticalimposedloads.SOLIDUNIT:Amasonryunitwhosenetcrosssectionalareainanyplaneparalleltothebearingsurfaceis75percentormoreofthegrosscrosssectionalareainthesameplane.STACKBOND:Abondinbearingandnonbearingwalls,exceptveneeredwalls,inwhichlessthan75percentof theunits inanytransverseverticalplane laptheendsoftheunitsbelowadistance lessthanonehalftheheightoftheunit,orlessthanonefourththelengthoftheunit.VENEEREDWALL:Awallinwhichthefacingisattachedtothebackingbutnotsobondedastoresultinacommonactionunderload.WALLJOINT:Averticaljointparalleltothefaceofthewall.WALLTIE:Ametalfastenerwhichconnectswythesofmasonrytoeachotherortoothermaterials.WYTHE:Portionofawallwhichisonemasonryunitinthickness.

7.2 Materials

7.2.1 GeneralAllmaterialsusedinmasonryconstructionshallconformtotherequirementsspecifiedinPart5ofthisCode.Ifnorequirementsarespecifiedforamaterial,qualityshallbebasedongenerallyacceptedgoodpractice,subjecttotheapprovalofthebuildingofficial.

7.2.2 MasonryUnitsThefollowingtypesofmasonryunitswhichconformtothestandardsmentionedinSec2.2.4ofPart5maybeusedinmasonryconstruction:

(a) Commonbuildingclaybricks(b) Burntclayhollowbricks(c) Burntclayfacingbricks(d) Hollowconcreteblocks

OthertypesofmasonryunitsconformingtoSec2.2.4ofPart5mayalsobeused.

7.2.3 MortarandGroutMortar and grout for masonry construction shall conform to the requirements specified in Part 5. MixproportionsandcompressivestrengthofsomecommonlyusedmortarsaregiveninTable6.7.1.

7.3 AllowableSTRESSES

7.3.1 GeneralStresses inmasonryshallnotexceed thevaluesgiven in thissection.Allallowablestresses forworkingstressdesignmaybeincreasedonethirdwhenconsideringwindorearthquakeforceseitheractingaloneorcombinedwithverticalloads.Noincreaseshallbeallowedforverticalloadsactingalone.

7.3.2 SpecifiedCompressiveStrengthofMasonry, f m Theallowablestressesformasonryconstructionshallbebasedonthevalueof f m asdeterminedbySec7.3.3below.


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Table6.7.1:MixProportionandStrengthofCommonlyusedMortars

GradeofMortar

MixProportionbyVolume1,2 MinimumCompressiveStrengthat28days,

N/mm2

Cement Sand

M1

M2

M3

M4

M5

M6

1

3

4

5

6

7

8

10

7.5

5

3

2

11.Sandandcementshallbemeasuredinloosevolumeandsandshallbewellgradedwitha

minimumF.M.of1.2.2.Limetoamaximumof

14 thpartbyvolumeofcementmaybeusedtoincreaseworkability.

7.3.3 Compliancewith Compliancewiththerequirementsforthespecifiedcompressivestrengthofmasonry, f m shallbeinaccordancewiththefollowing:

7.3.3.1 Masonry Prism Testing : The compressive strength of masonry based on tests at 28 days inaccordancewith"StandardTestMethodforCompressiveStrengthofMasonryPrisms",(ASTME447)

foreachsetofprismsshallequalorexceed f m .Verificationbymasonryprismtestingshallmeetthefollowing:

(a) TestingPrior toConstruction:A setof fivemasonryprisms shallbebuilt and tested inaccordancewithASTME447priortothestartofconstruction.Materialsusedforprismsshallbesameasusedintheproject.Prismsshallbeconstructedundertheobservationoftheengineeroranapprovedagencyandtestedbyanapprovedagency.

(b) TestingDuring Construction:When full allowable stresses are used in design, a set ofthreeprismsshallbebuiltandtestedduringconstructioninaccordancewith(ASTME447)for each 500 squaremeters ofwall area, but not less than one set of threemasonryprismsforanyproject.Notestingduringconstructionshallberequiredwhen50%oftheallowablestressesareusedindesign.

7.3.4 QualityControlQualitycontrolshallinclude,butnotbelimitedtoassurethat:

(a) Masonry units, reinforcement, cement, lime, aggregate and all other materials meet therequirements of the applicable standard of quality and that they are properly stored andpreparedforuse.

(b) Mortarandgroutareproperlymixedusingspecifiedproportionsofingredients.Themethodofmeasuringmaterials formortar and grout shall be such that proportions of materials arecontrolled.

(c) Construction details, procedures and workmanship are in accordance with the plans andspecification.

(d) Placement,splicesandbardiametersareinaccordancewiththeprovisionsofthischapterandtheplansandspecifications.

7.3.5 AllowableStressesinMasonryWhen the quality control provisions specified in Sec 7.3.4 above do not include requirements for specialinspection,theallowabledesignstressesinthissectionshallbereducedby50percent.

(a) CompressiveStress,Axial



i) Unreinforcedmasonrywalls,columnsandreinforcedmasonrywall

=

3

421

5 thfF ma

(7.3.1)

ii) Reinforcedmasonrycolumns

+=

3

421

5.15 thF

AAfF sc

e

sma

(7.3.2)

(b) CompressiveStress,Flexural

Fb = 0.33 f m 10N mm 2

(7.3.3)

(c) TensileStressforWalls,FlexureThe allowable tensile stress forwalls in flexure ofmasonry structureswithout tensilereinforcementusingmortarTypeM1orM2shallnotexceedthevaluesspecifiedinTables6.7.2and6.7.3.ForTypeM3andM4mortar,thevalueshallbereducedby25percent.

Notensionisallowedacrossheadjointsinstackbondmasonry.Valuesfortensionnormaltoheadjointsareforrunningbond.Thesevaluesshallnotbeusedforhorizontalflexuralmemberssuchasbeams,girdersorlintels.

Table6.7.2:FlexuralTension,Ft

Masonry NormaltoBedJoints

N/mm2

NormaltoHeadJointsN/mm2

SolidUnits

HollowUnits

0.20

0.12

0.40

0.25

Table6.7.3:TensionNormaltoHeadJoints,Ft

Masonry ClayUnits

N/mm2

ConcreteUnits

N/mm2

SolidUnits

HollowUnits

0.35

0.22

0.40

0.25

(d) ReinforcingBondStress,u PlainBars 0.30N/mm2

DeformedBars 1.0N/mm2 (e) ShearStressforFlexuralMembers,Fv

i) Whennoshearreinforcementisused

25.0083.0 = mv fF N/mm2 (7.3.4)

ii) Whenshearreinforcementisdesignedtotakeentireshearforce

75.025.0 = mv fF N/mm2 (7.3.5) (f) ShearStressforShearWalls,Fv

i) UnreinforcedmasonryForclayunits:


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40.0025.0 = mv fF N/mm2 (7.3.6) Forconcreteunits: M1orM2Mortar0.20N/mm2

M3Mortar 0.12N/mm2

ii) TheallowableshearstressforreinforcedmasonryshearwallsshallbeaccordingtoTable6.7.4.

7.3.6 AllowableStressesinReinforcement (a) TensileStressiDeformedbars,

165,5.0 = ys fF N/mm2 (7.3.7) ii)Ties,anchorsandplainbars,

135,4.0 = ys fF N/mm2 (7.3.8) Table6.7.4:AllowableShearStressforReinforcedMasonryShearWalls,Fv

M/Vd Fv,N/mm2 MaximumAllowableN/mm2

Masonry

takingall

shear



ofmasonry.Ifrequired,actualvaluesshallbeestablishedbytests.Thesevaluesarenottobereducedby50percentasspecifiedinSec7.3.5(a).

(a) ModulusofElasticityforMasonry

000,15750 = mm fE N/mm2 (7.3.12) (b) ModulusofElasticityforSteel

000,200=sE N/mm2 (7.3.13) (c) ShearModulusofMasonry

mEG 4.0= (7.3.14) 7.3.9 ShearandTensiononEmbeddedAnchorBolts

7.3.9.1 Allowable loads and placement requirements for anchor bolts shall be in accordance with thefollowing:

(a) Bentbaranchorboltsshallhaveahookwitha90degreebendwithaninsidediameterof3dbplusanextensionof1.5dbatthefreeend.

(b) Headedanchorboltsshallhaveastandardbolthead.(c) Plateanchorboltsshallhaveaplateweldedtotheshanktoprovideanchorageequivalentto

headedanchorbolts.

7.3.9.2 The effective embedment length, l b for bent bar anchors shall be the length of embedmentmeasured perpendicular from the surface of themasonry to the bearing surface of the bent endminus one anchor bolt diameter. For plate or headed anchor bolts l b shall be the length ofembedmentmeasuredperpendicularfromthesurfaceofthemasonrytothebearingsurfaceoftheplate or head of the anchorage. All bolts shall be grouted in placewith at least 25mm of groutbetween thebolt and themasonry except that6mmdiameterboltsmaybeplaced inbed jointswhichareatleasttwiceasthickasthediameterofthebolt.

7.3.9.3 AllowableShearForce

Allowable loads inshearshallbeaccording toTable6.7.5or lesserof thevalueobtained from thefollowingformulae:

( ) 4/11070 bmv AfB = (7.3.15) ybv fAB 12.0= (7.3.16)

Whenthedistance l beislessthan12db,thevalueofBvinEq(7.3.15)shallbereducedtozeroatadistance l be equal to 40mm.Where adjacent anchors are spaced closer than 8db, the allowableshearof theadjacentanchorsdeterminedbyEq (7.3.15)shallbe reducedby interpolation to0.75timestheallowableshearvalueatacentretocentrespacingof4db.

Table6.7.5:AllowableShear,BvforEmbeddedAnchorBoltsforMasonry,kN*

BentBarAnchorBoltDiameter,mm

f m N/mm2

10

12

16

20

22

25

28

10 2.0 3.7 5.9 7.9 8.5 9.1 9.6

12 2.0 3.7 5.9 8.2 8.3 9.5 10.1

13 2.0 3.7 5.9 8.5 9.2 9.8 10.4

17 2.0 3.7 5.9 8.5 9.7 10.3 11.0


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f m N/mm2

10

12

16

20

22

25

28

20 2.0 3.7 5.9 8.5 10.1 10.8 11.5

27 2.0 3.7 5.9 8.5 10.9 11.6 12.3

*ValuesareforboltsofatleastASTMA307quality.BoltsshallbethosespecifiedinSec

4.3.9.1.

7.3.9.4 AllowableTension

Allowable tension shallbe the lesservalue selected fromTable6.7.6and Table6.7.7or shallbedeterminedfromlesserofthevaluesobtainedfromthefollowingformulae:

mpt fAB = 04.0 (7.3.17) ybt fAB 2.0= (7.3.18)

TheareaAp shallbe the lesserof the areaobtained fromEq (7.3.17)and (7.3.18)andwhere theprojectedareasofadjacentanchorboltsoverlap,Apofeachanchorboltshallbereducedby50percentoftheoverlappingarea.

2

bpA l= (7.3.19)

2bepA l= (7.3.20)

Table6.7.6:AllowableTension,BtforEmbeddedAnchorBoltsforMasonry,kN1,2

EmbedmentLength,lb,orEdgeDistance,lbe,mm f m

N/mm2

50

75

100

125

150

200

250

10 1.0 2.4 4.3 6.7 9.7 17.3 27.0

12 1.2 2.6 4.7 7.4 10.6 18.9 29.6

13 1.2 2.8 5.0 7.8 11.2 20.0 31.2

17 1.3 3.1 5.6 8.7 12.6 22.4 35.0

20 1.5 3.4 6.7 9.5 13.8 24.5 38.2

27 1.7 3.9 7.0 11.0 15.9 28.3 44.11 Theallowabletensionvaluesarebasedoncompressivestrengthofmasonryassemblages.Whereyield

strengthofanchorboltsteelgoverns,theallowabletensionisgiveninTable6.7.7.2 ValuesareforboltsofatleastASTMA307quality.BoltsshallbethosespecifiedinSec7.3.9.1.

Table6.7.7:AllowableTension,BtforEmbeddedAnchorBoltsforMasonry,kN1


6 10 12 16 20 22 25 28

1.5 3.5 6.2 9.8 14.1 19.2 25.1 31.81 ValuesareforboltsofatleastASTMA307quality.BoltsshallbethosespecifiedinSec7.3.9.

7.3.9.5 CombinedShearandTension

Anchor bolts subjected to combined shear and tension shall be designed in accordancewith theformulagivenbelow:



00.1+v

v

t

t

Bb

Bb

7.3.22

7.3.9.6 MinimumEdgeDistance, l beTheminimumvalueof l bemeasuredfromtheedgeofthemasonryparalleltotheanchorbolttothesurfaceoftheanchorboltshallbe40mm.

7.3.9.7 MinimumEmbedmentDepth, l b

Theminimumembedmentdepth l bshallbe4dbbutnotlessthan50mm.

7.3.9.8 MinimumSpacingBetweenBolts

Theminimumcentretocentrespacingbetweenanchorsshallbe4db.

7.3.10 LoadTestForloadtest,themembershallbesubjecttoasuperimposedloadequaltotwicethedesignliveloadplusonehalfofthedeadload.Thisloadshallbemaintainedforaperiodof24hours.If,duringthetestoruponremovaloftheload,themembershowsevidenceoffailure,suchchangesormodificationsasarenecessarytomakethestructureadequatefortheratedcapacityshallbemade;orwherepossible,alowerratingshallbeestablished.Aflexuralmembershallbeconsidered tohavepassed the test if themaximumdeflectionat theendof the24

hourperiodneitherexceeds0.005 l nor0.00025 l2 t andthebeamandslabsshowarecoveryofatleast75per

centoftheobserveddeflectionwithin24hoursafterremovaloftheload.

7.3.11 ReuseofMasonryUnitsMasonryunitsmaybereusedwhenclean,unbrokenandconformstotherequirementsofPart5.Allstructuralpropertiesofmasonryofreclaimedunits,especiallyadhesionbond,shallbedeterminedbyapprovedtest.Theallowableworking stress shallnotexceed50per centof thatpermitted fornewmasonryunitsof the sameproperties.

7.4 BASICDESIGNREQUIREMENTS

7.4.1 GeneralMasonrystructuresshallbedesignedaccordingtotheprovisionsofthissection.Therequireddesignstrengthsofmasonrymaterialsandanyspecialrequirementsshallbespecifiedintheplansubmittedforapproval.

7.4.2 DesignConsiderations

7.4.2.1 Masonry structures shallbedesignedbasedonworking stress and linear stressstraindistribution.Requirements for working stress design of unreinforced and reinforced masonry structures areprovidedinSec4.5and4.6respectively.Inlieuoftheworkingstressdesignmethod,slenderwallsandshearwallsmaybedesignedbythestrengthdesignmethodspecifiedinSec7.7.

Thestructureshallbeproportionedsuchthateccentricityof loadingon themembers isassmallaspossible.Eccentricloadingshallpreferablybeavoidedbyproviding:

(a) adequatebearingoffloor/roofonthewalls

(b) adequatestiffnessinslabs,and

(c) fixityatthesupports.


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7.4.2.2 EffectiveHeight

(a) Wall :Theeffectiveheightofawall shallbe takenas theclearheightbetween the lateralsupportsattopandbottom inadirectionnormaltothe axisconsidered.Formembersnotsupportedatthetopnormaltotheaxisconsidered,theeffectiveheightistwicetheheightofthememberabove the support.Effectiveheight less than theclearheightmaybeused ifjustified.

(b) Column:Effectiveheightofthecolumnshallbetakenasactualheightforthedirectionitislaterallysupportedandtwicetheactualheightforthedirection it isnot laterallysupportedatthetopnormaltotheaxisconsidered.

(c) OpeninginWall:Whenopeningsoccurinawallsuchthatmasonrybetweentheopeningsisbydefinitionacolumn,effectiveheightofmasonrybetweentheopeningsshallbeobtainedasfollows:

i) When wall has full restraint at the top, effective height for the directionperpendicular to the plane ofwall equals 0.75H plus 0.25H',where H is thedistance between supports and H' is the height of the taller opening; andeffectiveheightforthedirectionparalleltothewallequalsH.

ii) Whenwallhaspartialrestraintat the topandbottom,effectiveheight for thedirection perpendicular to the plane ofwall equalsHwhen height of neitheropeningexceeds0.5Handitisequalto2Hwhenheightofanyopeningexceeds0.5H; and effective height for the direction parallel to the plane of thewallequals2H.

7.4.2.3 EffectiveLength

EffectivelengthofawallfordifferentsupportconditionsshallbeasgiveninTable6.7.8.

7.4.2.4 EffectiveThickness

Theeffectivethicknessofwallsandcolumnsforuse inthecalculationofslendernessratio,shallbedefinedasfollows:(a) SolidWalls:Theeffectivethicknessofsolidwalls,facedwallsorgroutedwallsshallbethe

specifiedthicknessofthewall.(b) SolidWalls with RakedMortar Joints: The effective thickness of solid walls with raked

mortarjointsshallbetheminimumthicknessmeasuredatthejoint.(c) Cavity Walls: When both limbs of a cavity wall are axially loaded, each limb shall be

consideredindependentlyandtheeffectivethicknessofeachlimbshallbedeterminedasin(a)or(b)above.Ifoneofthelimbsisaxiallyloaded,theeffectivethicknessofthecavitywallshallbetakenasthesquarerootofthesumofthesquaresoftheeffectivethicknessesofthelimbs.

(d) WallsStiffenedbyPilasters:Whensolidorcavitywallsarestiffenedbypilastersatintervals,theeffective thickness tobeused for thecalculationofh'/t ratio shallbedeterminedasfollows:

i) Solid Walls: For stiffened solid walls the effective thickness shall be the specifiedthicknessmultipliedbythestiffeningcoefficient,k,valuesofwhicharegivenbelow:

pp wl

StiffeningCoefficient,k*

wp tt

1 2 3

6 1.0 1.4 2.0

8 1.0 1.3 1.7

10 1.0 1.2 1.4

15 1.0 1.1 1.2

20ormore 1.0 1.0 1.0



*Linearinterpolationispermittedforobtainingintermediatevaluesofk

where, l p = centretocentrespacingofpilasters

tp = thicknessofpilasterincludingthewall

tw = specifiedthicknessofmainwall

wp = widthofpilasterinthedirectionofwall

ii) CavityWalls:When one or both limbs of a cavitywall are adequately bonded intopilasters at intervals, the effective thickness of each limb shall be determinedseparatelyasin(a),(b)ord(i)aboveandtheeffectivethicknessofthestiffenedcavitywallshallbedeterminedinaccordancewith(c)above.Where slenderness ratio of thewall is based on the effective length, the effectivethicknessshallbethesameasthatwithoutpilasters.

(e) Columns: The effective thickness for rectangular columns in the direction considered is theactualthicknessprovidedinthatdirection.Theeffectivethicknessfornonrectangularcolumnsis the thicknessof a square columnwith the samemomentof inertia about its axis as thatabouttheaxisconsideredintheactualcolumn.

Table6.7.8:EffectiveLengthofWalls

SupportCondition EffectiveLength

Whereawalliscontinuousandissupportedbycrosswallandthere

isnoopeningwithinadistanceofH/8fromthefaceofcrosswall,

Or

Whereawalliscontinuousandissupportedbypier/buttresses

conformingtoSec7.4.3.3(c)(ii).

0.8L

Whereawallissupportedbycrosswallatoneendandcontinuous

withcrosswallatotherend,

Or

Whereawallissupportedbypier/buttressesatoneendand

continuouswithpier/buttressesatotherendconformingto

Sec7.4.3.3(c)(ii).

0.9L

Whereawallissupportedateachendbycrosswall,

Or

Whereawallissupportedateachendbypier/buttresses

conformingtoSec7.4.3.3(c)(ii).

1.0L

Whereawallisfreeatoneendandcontinuouswithacrosswallat

theotherend,

Or

Whereawallisfreeatoneendandcontinuouswitha

pier/buttressesattheotherendconformingtoSec7.4.3.3(c)(ii).

1.5L

Whereawallisfreeatoneendandsupportedattheotherendby

acrosswall,

Or

Whereawallisfreeatoneendandsupportedattheotherendbya

pier/buttressesconformingtoSec7.4.3.3(c)(ii).

2.0L


6378 Vol.2

7.4.2.5 SlendernessRatio

(a) Walls: For a wall, slenderness ratio shall be the ratio of effective height to effectivethickness or effective length to effective thickness whichever less is. In case of a loadbearingwall,slendernessratioshallnotexceed20.

(b) Column: Foracolumn, slenderness ratio shallbe taken tobe thegreaterof the ratioofeffective heights to the respective effective thickness in the two principal directions.Slendernessratioforaloadbearingcolumnshallnotexceed12.

7.4.2.6 EffectiveArea

Theeffectivecrosssectionalareashallbebasedontheminimumbeddedareaofthehollowunits,orthe gross areaof solidunitsplus any grouted area. Ifhollowunits areusedperpendicular to thedirectionofstress, theeffectiveareashallbe lesserof theminimumbeddedareaor theminimumcrosssectional area. If bed joints are raked, the effective area shall be correspondingly reduced.Effectiveareasforcavitywallsshallbethatoftheloadedwythes.

7.4.2.7 FlexuralResistanceofCavityWalls

Forcomputing the flexural resistance, lateral loadsperpendicular to theplaneof thewall shallbedistributedtothewythesaccordingtotheirrespectiveflexuralrigidities.

7.4.2.8 EffectiveWidthofIntersectingWalls

Whereashearwallisanchoredtoanintersectingwallorwalls,thewidthoftheoverhangingflangeformedbytheintersectedwallsoneithersideoftheshearwallshallnotexceed6timesthethicknessof the intersectedwall.Limitsof theeffective flangemaybewaived if justified.Only theeffectiveareaofthewallparalleltotheshearforcesmaybeassumedtocarryhorizontalshear.

7.4.3 Supports

7.4.3.1 VerticalSupport

Structuralmembersprovidingverticalsupportofmasonryshallprovideabearingsurfaceonwhichtheinitialbedjointshallnotbelessthan6mmormorethan25mmandshallbeofnoncombustiblematerials,exceptwheremasonryisanonstructuraldecorativefeatureorwearingsurface.

7.4.3.2 VerticalDeflection

Elements supportingmasonry shall be designed so that their vertical deflection does not exceed1/600oftheclearspanundertotalloads.Lintelsshallbesupportedoneachendsuchthatallowablestressesinthesupportingmasonryarenotexceeded.Theminimumbearinglengthshallbe100mm.

7.4.3.3 LateralSupport

(a) Lateralsupportofmasonrymaybeprovidedbycrosswalls,columns,piers,counterfortsorbuttresses when spanning horizontally or by floors, beams or roofs when spanningvertically.

(b) Lateral supports for a masonry element such as load bearing wall or column shall beprovidedtoi) limit the slendernessofamasonryelementsoas topreventor reducepossibilityof

bucklingofthememberduetoverticalloads;andii) resist the horizontal components of forces so as to ensure stability of a structure

againstoverturning.(c) From consideration of slenderness (i.e. requirement b(i) above),masonry elementsmay be

consideredtobelaterallysupportedifi) incaseofawall,whereslendernessratio isbasedoneffectiveheight,floor/roofslab

(orbeamsandslab)irrespectiveofthedirectionofspan,bearsonthesupportedwallaswellascrosswalls,totheextentofatleast100mm;



ii) in case of a wall, when slenderness ratio is based on its effective length, a crosswall/pier/buttress of thickness equal to or more than half the thickness of thesupportedwallor125mm,whichever ismoreandaverage lengthequal toormorethanonefifthoftheheightofthewall,isbuiltatrightangletothewallandproperlybonded;

iii) incaseofacolumn,anRCor timberbeam/RS joist/roof truss, is supportedon thecolumn.Inthiscase,thecolumnwillnotbeconsideredtobelaterallysupportedinthedirectionatrightangletoit;and

iv) in case of a column, anRC beam forming a part of beam and slab construction, issupported on the column, and the slab adequately bears on stiffening walls. Thisconstruction will provide lateral support to the column, in the direction of bothhorizontalaxes.

7.4.4 StabilityAwallorcolumnsubject toverticaland lateral loadsmaybeconsidered toprovideadequate lateralsupportfrom considerationof stability, if the constructionproviding the support is capableof resisting the followingforces:

(a) Simplestaticreactionsatthepointoflateralsupporttoallthelateralloads;plus(b) A lateral load equal to 2.5% of the total vertical load that the wall or column is

designatedtocarryatthepointoflateralsupport.

7.4.4.1 Incaseofloadbearingbuildingsuptofivestoreys,stabilityrequirementsmaybeconsideredtohavebeensatisfiedifthefollowingconditionsaremet.

(a) Heighttowidthratioofbuildingdoesnotexceed2.(b) Crosswallsactingasstiffeningwallscontinuousfromouterwalltoouterwallorouterwalltoa

loadbearinginnerwall,andofthicknessandspacingasgiveninTable6.7.9areprovided.Note:Ifstiffeningwallorwallsthatareinaline,areinterruptedbyopenings,lengthofsolidwallorwallsinthezoneofthewallthatistobestiffenedshallbeatleastonefifthoftheheightoftheopening.

(c) Floorsandroofeitherbearoncrosswallsorareproperlyanchoredtothosewallssuchthatalllateralloadsaresafelytransmittedtothosewallsandthroughthemtothefoundation.

(d) Crosswallsarebuiltjointlywiththebearingwallsand jointlymortared,or interconnectedbytoothing.

Note:Crosswallsmaybeanchored towalls tobe supportedby tiesofnoncorrosivemetalofminimum section6x35mmandlength60mmwithendsbentatleast50mm,maximumverticalspacingoftiesbeing1.2m.

Table6.7.9:ThicknessandSpacingofStiffeningWalls

StiffeningWall*

ThicknessofLoad

BearingWalltobe

StoreyHeightnot

toExceed

Thicknessnotlessthan Maximum

spacing

Stiffened

(mm)

(m)

1to3storeys

(mm)

4and5storeys

(mm)

(m)

100

200

300

above300

3.2

3.2

3.4

5.0

100

100

100

100

200

200

200

4.5

6.0

8.0

8.0

*Storeyheightandmaximumspacingasgivenarecentretocentredimensions.


6380 Vol.2

7.4.4.2 Incaseofwallsexceeding 8.0m in length,safetyandadequacyof lateralsupportsshallalwaysbecheckedbystructuralanalysis.

7.4.4.3 Atrussedroofingmaynotprovidelateralsupportunlessspecialmeasuresareadoptedtobraceandanchortheroofing.However, incaseofresidentialandsimilarbuildingsofconventionaldesignwithtrussedroofinghavingcrosswalls,itmaybeassumedthatstabilityrequirementsaremetbythecrosswallsandstructuralanalysisforstabilitymaybedispensedwith.

7.4.4.4 Incaseofwallsexceeding 8.0m in length,safetyandadequacyof lateralsupportsshallalwaysbecheckedbystructuralanalysis.

7.4.4.5 Atrussedroofingmaynotprovidelateralsupportunlessspecialmeasuresareadoptedtobraceandanchortheroofing.However, incaseofresidentialandsimilarbuildingsofconventionaldesignwithtrussedroofinghavingcrosswalls,itmaybeassumedthatstabilityrequirementsaremetbythecrosswallsandstructuralanalysisforstabilitymaybedispensedwith.

7.4.4.6 In case of external walls of basement and plinth, stability requirements of Sec 7.4.4 may beconsideredtobesatisfiedif:

(a) Bricksusedinbasementandplinthhaveaminimumcrushingstrengthof5N/mm2andmortarusedinmasonryisofTypeM3orbetter,

(b) Clearheightofceilinginbasementdoesnotexceed2.6m,(c) Inthezoneofactionofsoilpressureonbasementwalls,traffic loadexcludinganysurcharge

duetoadjoiningbuildingsdoesnotexceed5kN/m2,(d) MinimumthicknessofbasementwallsisinaccordancewithTable6.7.10.

Incase there issurchargeonbasementwalls fromadjoiningbuildings, thicknessofbasementwallsshallbebasedonstructuralanalysis.

Table6.7.10:MinimumThicknessofBasementWall

MinimumThicknessof

BasementWall

(Nominal),mm

HeightoftheGroundaboveBasement

FloorLevelwithWallLoading

(PermanentLoad),m

Lessthan50kN/m Morethan50kN/m

375

250

2.0

1.4

2.5

1.8

7.4.4.7 FreeStandingWall

Free standingwalls, subject towind pressure or seismic forces shall be designed on the basis ofpermissible tensile stress inmasonryor stabilityconsideration.However inSeismicZones1and2,free standingwallsmaybeproportionedwithoutmaking anydesign calculationswith thehelpofTable6.7.11providedthemortarusedisoftypenotleanerthanM3.ForparapetwallseeSec7.4.9.4.

7.4.5 StructuralContinuityIntersectingstructuralelementsintendedtoactasaunitshallbeanchoredtogethertoresistthedesignforces.Wallsshallbeanchoredtogethertoallfloors,roofsorotherelementswhichprovidelateralsupportforthewall.Wherefloorsorroofsaredesignedtotransmithorizontalforcestowalls,theanchoragestothewallsshallbedesignedtoresistthehorizontalforces.



Table6.7.11:HeighttoThicknessRatioofFreeStandingWall

DesignWindPressure,N/m2 HeighttoThicknessRatio

Upto300

600

900

1100

10

7

5

4

Note: Heightistobetakenfrom150mmbelowgroundlevelortopoffooting/foundation

block,whicheverishigher,anduptothetopedgeofthewall.

7.4.5.1 MultiwytheWalls

All wythes shall be bonded by grout or tied together by corrosion resistant wall ties or jointreinforcementasfollows:(a) WallTies inCavityWallConstruction:Wall ties shallbeof sufficient length toengageall

wythes. Theportionof thewall tieswithin thewythe shallbe completely embedded inmortar or grout. The ends of the wall ties shall be bent to 90 degree angles with anextensionnotlessthan50mmlong.Walltiesnotcompletelyembeddedinmortarorgroutbetweenwythesshallbeasinglepiecewitheachendengagedineachwythe.Thereshallbeatleastone6mmdiameterwalltieforeach0.45m2ofwallarea.Forcavitywallsinwhichthewidthofthecavityisgreaterthan75mm,butnotmorethan115mm,atleastone6mmdiameterwalltieforeach0.3m2ofwallareashallbeprovided.Ties in alternate courses shallbe staggered. The verticaldistancebetween ties shallnotexceed600mm.Thehorizontaldistancebetweentiesshallnotexceed900mm.Additional tiesspacednotmore than900mmapartshallbeprovidedaroundandwithin300mmoftheopening.Wall ties of different size and spacingmay be used if they provide equivalent strengthbetweenwythes.

(b) WallTiesforGroutedMultiwytheConstruction:Thetwowythesshallbebondedtogether

withat least6mmdiametersteelwalltiesforeach0.20m2ofarea.Walltiesofdifferentsizeandspacingmaybeusediftheyprovideequivalentstrengthbetweenwythes.

(c) Joint Reinforcement: Prefabricated joint reinforcement for masonry walls shall have aminimumofonecrosswireofatleast3mmdiametersteelforeach0.2m2ofwallarea.Theverticalspacingofthejointreinforcementshallnotexceed400mm.Thelongitudinalwiresshallbethoroughlyembeddedinthebedjointmortar.Thejointreinforcementshallengageallwythes.Wherethespacebetweentiedwythesisfilledwithgroutormortar,theallowablestressesandotherprovisions formasonrybondedwallsshallapply.Where thespace isnot filled,tiedwallsshallconformtotheallowablestress,lateralsupport,thickness(excludingcavity),heightandtierequirementsofcavitywalls.

7.4.6 JointReinforcementandProtectionofTiesTheminimummortar coverbetween tiesor joint reinforcementandanyexposed face shallbe15mm.Thethicknessofgroutormortarbetweenmasonryunitsandjointreinforcementshallnotbelessthan6mm,exceptthatsmallerdiameterreinforcementorboltsmaybeplacedinbedjointswhichareatleasttwiceasthickasthediameterofthereinforcement.

7.4.7 PipesandConduitsPipeorconduitshallnotbeembeddedinanymasonrysoastoreducethecapacitytolessthanthatnecessaryforrequiredstabilityorrequiredfireprotection,exceptthefollowing:

(a) Rigid electrical conduitmay be embedded in structuralmasonrywhen their location has beendetailedontheapprovedplan.


6382 Vol.2

(b) Anypipeorconduitmaypassverticallyorhorizontallythroughanymasonrybymeansofasleeveatleastlargeenoughtopassanyhuborcouplingonthepipeline.Suchsleevesshallnotbeplacedcloser than three diameters, centre to centre, nor shall they unduly impair the strength ofconstruction.

(c) Placementofpipesorconduitsinunfilledcoresofhollowunitmasonryshallnotbeconsideredasembedment.

7.4.8 LoadsandLoadCombination

7.4.8.1 DesignLoads

Alldesign loadsandotherforcestobetakenforthedesignofmasonrystructuresshallconformtoChapter2,Loads.

7.4.8.2 LoadDispersion

Theangleofdispersionofverticalloadonwallsshallbetakenasnotmorethan30ofromthevertical.

7.4.8.3 DistributionofConcentratedVerticalLoadsinWalls

The length ofwall, laid up in running bond,whichmay be considered capable ofworking at themaximumallowablecompressivestressestoresistverticalconcentrated loads,shallnotexceedthecentretocentredistancebetweensuchloads,northewidthofbearingareaplusfourtimesthewallthickness. Concentrated vertical loads shall not be assumed distributed across continuous verticalmortarorcontrol jointsunlesselementsdesigned todistribute theconcentratedvertical loadsareemployed.

7.4.8.4 LoadsonNonbearingWall

Masonrywallsusedasinteriorpartitionorasexteriorsurfacesofbuildingwhichdonotcarryverticalloadsimposedbyotherelementsofthebuildingshallbedesignedtocarrytheirownweightplusanysuperimposedfinishandlateralforces.Bondingoranchorageofnonbearingwallsshallbeadequatetosupportthewallsandtotransferlateralforcestothesupportingstructures.

7.4.8.5 LoadCombinations

LoadcombinationfordesignofmasonrystructuresshallconformtotherequirementsofSec2.7.5.1.

7.4.9 MinimumDesignDimensions

7.4.9.1 MinimumThicknessofLoadBearingWalls

Thenominalthicknessofmasonrybearingwallsinbuildingshallnotbelessthan250mm. Exception:

Stiffenedsolidmasonrybearingwallsinonestoreybuildingsmayhaveaminimumeffectivethicknessof165mmwhennotover3minheight,providedthatwhengableconstructionisusedanadditional1.5mheightmaybepermittedatthepeakofthegable.

7.4.9.2 VariationinThickness

Whenachangeinthicknessduetominimumthicknessrequirementsoccursbetweenfloorlevels,thegreaterthicknessshallbecarrieduptothehigherfloorlevel.

7.4.9.3 DecreaseinThickness

Whenwallsofmasonryofhollowunitsormasonrybondedhollowwallsaredecreasedinthickness,acourseorcoursesofsolidmasonryshallbeconstructedbetweenthewallsbelowandthethinnerwallabove,orspecialunitsorconstructionshallbeusedtotransmitthe loadsfromwythestothewallsbelow.

7.4.9.4 ParapetWall

Parapetwallsshallbeat least200mmthickandheightshallnotexceed4timesthethickness.Theparapetwallshallnotbethinnerthanthewallbelow.



7.5 DESIGNOFUNREINFORCEDMASONRY

7.5.1 GeneralThe requirementsof this section are applicable tounreinforcedmasonry in addition to the requirementsofSec7.4.

7.5.2 DesignofMembersSubjectedtoAxialCompressionThestressesdue tocompressive forcesappliedat thecentroidofany loadbearingwall,columnandpilastermaybecomputedbyEq(7.5.1)belowassuminguniformdistributionovertheeffectivearea.

e

a APf = 7.5.1

7.5.3 DesignofMembersSubjectedtoCombinedBendingandAxialCompression

(a) Compressivestressesduetocombinedbendingandaxial loadshallsatisfy therequirementsofSec7.3.5.

(b) Resultant tensilestressduetocombinedbendingandaxial loadshallnotexceedtheallowableflexuraltensilestress,FtasspecifiedinSec7.3.

7.5.4 DesignofMembersSubjectedtoFlexureStressesduetoflexurecalculatedbyEq(7.5.2)belowshallnotexceedthevaluesgiveninSec7.3.5.

IMcfb = 7.5.2

7.5.5 DesignofMembersSubjectedtoShearShearcalculationsinflexuralmembersandshearwallsshallbebasedonEq(7.5.3)below.

ev A

Vf = 7.5.3

7.5.6 DesignofArchesGeometrical formand thecrosssectionaldimensionsofmasonryarchshallbe selected such that the lineofthrustatanysectionofthearchiskeptwithinthemiddlethirdofthesectionofthearchrib.Theelastictheoryofarches shallbepermitted for theanalysisofunreinforcedmasonryarches.All supportsofarches shallbecapableofdevelopingtherequiredhorizontalthrustwithoutsufferingunacceptabledisplacements.Everyarchmustbedesignedtoresistthestressesduetothefollowingloads:

(a) GravityLoads:i. Deadloadsshallbeplacedinconformitywiththeiractualdistribution.ii. Liveloadsshallbepositionedtocoverentirespanorpartofthespanasnecessaryto

produce themaximum stressesat thecrown,springingandallother sectionsof thearchrib.

(b) Loadsduetotemperaturechange.(c) Shrinkageloadduetosettingandhardening. (d) Shorteningofarchribunderthrustcausedbyloads.

7.5.7 FootingsandCorbelsTheslopeoffootingandcorbelling(measuredfromthehorizontaltothefaceofthecorbelledsurface)shallnotbelessthan60degrees.Themaximumhorizontalprojectionof corbelling from theplaneof thewall shallbe such that stressatanysectiondoesnotexceedtheallowablevalue.


6384 Vol.2

7.6 DESIGNOFREINFORCEDMASONRY

7.6.1 GeneralTherequirementsofthissectionare inadditiontothosespecified inSec7.4andareapplicabletoreinforcedmasonry.Plainbarslargerthan6mmindiametershallnotbeused.

7.6.1.1 Assumptions

Thefollowingassumptionsshallbeapplicableforthissection.(a) Masonrycarriesnotensilestress.(b) Reinforcementiscompletelysurroundedbyandbondedtomasonrymaterialsothattheywork

togetherasahomogeneousmaterialwithintherangeofworkingstresses.

7.6.2 DesignofMembersSubjectedtoAxialCompressionStressesdue tocompressive forcesappliedat thecentroidof loadbearingwall,columnandpilastermaybecomputed assuming uniform distribution over the effective area. Stress shall be calculated from Eq(7.6.1)below:

ea A

Pf = 7.6.1

7.6.3 DesignofMembersSubjectedtoCombinedBendingandAxialCompressionStressduetocombinedbendingandaxial loadsshallsatisfytherequirementsofSec7.3.5.Columnsandwallssubjectedtobendingwithorwithoutaxialloadsshallmeetallapplicablerequirementsforflexuraldesign. Thedesignofwallswithan(h//t)ratiolargerthan30shallbebasedonforcesandmomentsdeterminedfromanalysis of structure. Such analysis shall take into account influence of axial loads and variablemoment ofinertia onmember stiffness and fixed endmoments, effect of deflections onmoments and forces, and theeffectsofdurationofloads.

7.6.4 DesignofMembersSubjectedtoShearForceShearingstressesinflexuralmembersandshearwallsshallbecomputedby

bjdVfv = 7.6.2

When the computed shear stress exceeds the allowable value, web reinforcement shall be provided anddesignedtocarrythetotalshearforce.Bothverticalandhorizontalshearstressesshallbeconsidered.ThearearequiredforshearreinforcementplacedperpendiculartothelongitudinalreinforcementshallbecomputedbyEq(7.6.3)below:

dFsVA

sv = 7.6.3

Spacingofverticalshearreinforcementshallnotexceedd/2,nor600mm. Inclinedshearreinforcementshallhave amaximum spacing of 0.375 d (1+ cot ), but not greater than 600mm,where is the acute anglebetweeninclinedbarandthehorizontal.

7.6.5 DesignofMembersSubjectedtoFlexuralStress

7.6.5.1 RectangularElements

Rectangularflexuralelementsshallbedesignedinaccordancewiththefollowingequationsorothermethodsbasedonthesimplifiedassumptions.

(a) Compressivestressinthemasonry:

=

jkbdMfb

22 7.6.4



(b) Tensilestressinthelongitudinalreinforcement:

jdAMfs

s = 7.6.5 (c) Designcoefficients:

( )[ ] npnpnpk += 2/12 2 7.6.6 or

b

s

nffk +

=1

1 7.6.7

31 kj = 7.6.8

7.6.5.2 NonrectangularSections

Flexural elements of nonrectangular crosssection shall be designed in accordance with theassumptionsgiveninSec7.4.2.1and7.6.1.1.

7.6.5.3 LateralSupport

Thecleardistancebetween lateralsupportsofabeamshallnotexceed32timesthe leastdepthofcompressionarea.

7.6.5.4 EffectiveWidth

Incomputingflexuralstresses inwallswherereinforcementoccurs,theeffectivewidthassumedforrunningbondmasonryshallnotexceed6 times thenominalwall thicknessor thecentre tocentredistancebetweenreinforcement.Wherestackbondisused,theeffectivewidthshallnotexceed3times the nominalwall thickness or the centre to centre distance between reinforcement or thelengthofoneunit,unlessgroutedsolidusingopenendedjoints.

7.6.5.5 Bond

In flexuralmembers inwhich tensile reinforcement is parallel to the compressive face, the bondstressshallbecomputedbytheformula:

= jdVu

o 7.6.9

7.6.6 ReinforcementRequirementsandDetails

7.6.6.1 ColumnReinforcement

(a) VerticalReinforcement:Theareaofverticalreinforcementshallnotbe less than0.005Aeandnotmorethan0.04Ae.Atleastfour10mm barsshallbeprovided.

(b) Lateral Ties: All longitudinal bars for columns shall be enclosed by lateral ties. Lateralsupportshallbeprovidedtothelongitudinalbarsbythecornerofacompletetiehavinganincludedangleofnotmorethan135degreesorbyahookattheendofatie.Thecornerbars shallhave such supportprovidedby a complete tie enclosing the longitudinalbars.Alternatelongitudinalbarsshallhavesuchlateralsupportprovidedbytiesandnobarshallbefartherthan150mmfromsuchalaterallysupportedbar.Lateral tiesand longitudinalbarsshallbeplacednot less than40mmandnotmore than125mm,fromthesurfaceofthecolumn.Lateraltiesmaybeagainstthelongitudinalbarsorplaced inthehorizontalbed joint iftherequirementsofSec4.4.6aremet.Spacingoftiesshallnotbemorethan16timeslongitudinalbardiameter,48timestiebardiameterortheleastdimensionofthecolumnbutnotmorethan450mm.


6386 Vol.2

Tiesshallbeatleast6mmindiameterfor22mmdiameterorsmallerlongitudinalbarsand10mm indiameter for larger longitudinalbars.Ties lessthan10mm indiametermaybeusedforlongitudinalbarslargerthan22mmindiameter,providedthetotalcrosssectionalareaofsuchsmallertiescrossinga longitudinalplane isequalto thatofthe largertiesattheirrequiredspacing.

(c) AnchorBoltTies:Additionaltiesshallbeprovidedaroundanchorboltswhicharesetinthetopof thecolumn.Such tiesshallengageat least fourboltsor,alternativelyat least fourverticalcolumnbarsoracombinationofboltsandbarstotalingfour innumber.Suchtiesshall be locatedwithin the top 125mm of the column and shall provide a total of 250squaremillimetersormore incrosssectionalarea.Theuppermosttiesshallbewithin50mmofthetopofthecolumn.

7.6.6.2 MaximumReinforcementSize

Themaximumsizeofreinforcingbarsshallbe35mm.Maximumsteelareaincellshallbe6percentofthecellareawithoutsplicesand12percentofcellareawithsplices.

7.6.6.3 SpacingofLongitudinalReinforcement

The clear distance between parallel bars, except in columns, shall not be less than the nominaldiameterof thebarsor25mm,except thatbars in a splicemaybe in contact.This cleardistancerequirementappliestothecleardistancebetweenacontactspliceandadjacentsplicesorbars.Theminimum cleardistancebetweenparallelbars in columns shallbe two andonehalf times thebardiameter.Thecleardistancebetweenthesurfaceofabarandanysurfaceofamasonryunitshallnotbe lessthan6mm for finegroutand12mm for coarsegrout.Crosswebsofhollowunitsmaybeusedassupportforhorizontalreinforcement. All reinforcingbars,except joint reinforcing, shallbe completely embedded inmortaror grout andhaveaminimumcover,includingthemasonryunit,asspecifiedbelow:(a) 20mmwhennotexposedtoweather(b) 40mmwhenexposedtoweather(c) 50mmwhenexposedtosoil

7.6.6.4 AnchorageofFlexuralReinforcement

(a) The tensionorcompression inanybaratanysectionmustbedevelopedoneachsideofthatsectionbytherequireddevelopment length.Thedevelopment lengthofthebarmaybe achievedby a combination of an embedment length, anchorageor, for tensiononly,hooks.Therequireddevelopmentlengthfordeformedbarsordeformedwiresshallbecalculatedby:

sbd fd29.0=l forbarsintension (7.6.10) sbd fd22.0=l forbarsincompression (7.6.11)

Developmentlengthforplainbarsshallbe2.0timesthelengthcalculatedbyEq(7.6.10).

(b) Exceptatsupports,oratthefreeendofcantilevers,everyreinforcingbarshallbeextendedbeyondthepointatwhichitisnolongerneededtoresisttensilestressforadistanceequalto12bardiametersorthedepthoftheflexuralmember,whicheverisgreater.Noflexuralbarsshallbeterminatedinatensilezoneunlessoneofthefollowingconditionsissatisfied:

i) The shear is not over onehalf of that permitted, including allowance for shearreinforcement,ifany.

ii) Additional shear reinforcement in excess of that required is provided eachwayfromthecutoffadistanceequaltothedepthofthebeam.Theshearreinforcement



spacingshallnotexceedd/8rb,whererbistheratiooftheareaofbarscutofftothetotalareaofbarsatthesection.

iii)Thecontinuingbarsprovidedouble thearearequired for flexureat thatpointordoubletheperimeterrequiredforreinforcingbond.

(c) Atleastonethirdofthetotalreinforcementprovidedfornegativemomentatthesupportshall be extended beyond the extreme position of the point of inflection a distancesufficient todeveloponehalf the allowable stress in thebar, one sixteenthof the clearspan,orthedepthdofthemember,whicheverisgreater.

(d) Tensile reinforcement of negative moment in any span of a continuous restrained orcantilever beam, or in any member of a rigid frame, shall be adequately anchored byreinforcingbond,hooksormechanicalanchorsinorthroughthesupportingmember.

(e) Atleastonethirdoftherequiredpositivemomentreinforcementinsimplebeamsoratthefreelysupportedendofcontinuousbeamsshallextendalong thesame faceof thebeaminto the support at least 150mm.At least one fourth of the required positivemomentreinforcementatthecontinuousendofcontinuousbeamsshallextendalongthesamefaceofthebeamintothesupportatleast150mm.

(f) Compression reinforcement in flexuralmembers shallbeanchoredby tiesor stirrupsnotless than 6mm in diameter, spaced not farther apart than 16 bar diameters or 48 tiediameterswhicheverissmaller.Suchtiesorstirrupsshallbeusedthroughoutthedistancewherecompressionsteelisrequired.

(g) Inregionsofmomentwherethedesigntensilestressesinthesteelaregreaterthan80percentoftheallowablesteeltensilestress(Fs),thelaplengthofsplicesshallbeincreasednotless than50per centof theminimum required length.Otherequivalentmeansof stresstransfertoaccomplishthesame50percentincreasemaybeused.

7.6.6.5 AnchorageofShearReinforcement

(a) Singleseparatebarsusedasshearreinforcementshallbeanchoredateachendbyoneofthefollowingmethods:

i) Hookingtightlyaroundthelongitudinalreinforcementthrough180degrees.

ii) Embedment above or below the middepth of the beam on the compression side adistancesufficienttodevelopthestressinthebarforplaneordeformedbars.

iii) Byastandardhook(seeSec4.6.6.6)consideredasdeveloping50N/mm2,plusembedmentsufficient to develop the remainder of the stress to which the bars are subject. Theeffectiveembeddedlengthshallnotbeassumedtoexceedthedistancebetweenthemiddepthofthebeamandthetangentofthehook.

(b) The ends of bars forming single U ormultiple U stirrups shall be anchored by one of themethods specified above or shall be bent through an angle of at least 90 degrees tightlyaroundalongitudinalreinforcingbarnotlessindiameterthanthestirrupbar,andshallprojectbeyondthebendatleast12diametersofthestirrup.

(c) TheloopsorclosedendsofsingleUormultipleUstirrupsshallbeanchoredbybendingaroundthelongitudinalreinforcementthroughanangleofatleast90degreesandprojectbeyondtheendofthebendatleast12diametersofthestirrup.

7.6.6.6 Hooks

(a) Theterm"standardhook"shallmeanoneofthefollowing:i. A180degreeturnplusanextensionofat least4bardiametersbutnot lessthan65mmatthefreeendofthebar.

ii. 90degree turnplusanextensionofat least12bardiametersat the freeendof thebar.


6388 Vol.2

iii. For stirrupand tieanchorageonlyeithera90degreeora135degree turn,plusanextensionofat least6bardiametersbutnot lessthan65mmatthefreeendofthebar.

(b) Thediameterofbendmeasuredonthe insideofthebarotherthanstirrupsandties,shallnotbelessthanthatsetforthinTable6.4.12.

(c) Insidediameterofbend for12mmdiameterorsmallerstirrupsand tiesshallnotbe lessthan4bardiameters.Insidediameterofbendfor16mmdiameterorlargerstirrupsandtiesshallnotbelessthanthatgiveninTable6.4.12.

(d) Hooks shallnotbepermitted in the tensionportionof anybeam, except at the endsofsimple or cantilever beams or at the freely supported ends of continuous or restrainedbeams.

Table6.4.12:MinimumDiameterofBend

BarDiameter MinimumDiameterofBend

1 6mmthrough25mm2 8mm through35mm

6bardiameters

8bardiameters

(e) Hooksshallnotbeassumedtocarryaloadwhichwouldproduceatensilestressinthebargreaterthan50N/mm2.

(f) Hooksshallnotbeconsideredeffectiveinaddingtothecompressiveresistanceofbars.(g) Anymechanicaldevicecapableofdevelopingthestrengthofthebarwithoutdamagetothe

masonrymaybeused in lieuofahook.Datamustbepresentedtoshowtheadequacyofsuchdevices.

7.6.6.7 Splices

The amount of lap of lapped splices shall be sufficient to transfer the allowable stress of thereinforcementas inSec4.6.6.4. Innocaseshallthe lengthofthe lappedsplicebe lessthan30bardiametersforcompressionand40bardiametersfortension.Weldedormechanicalconnectionsshalldevelop125percentofthespecifiedyieldstrengthofthebarintension,exceptforconnectionsofcompressionbarsincolumnsthatarenotpartoftheseismicsystemandarenotsubjecttoflexure,wherethecompressivestrengthonlyneedbedeveloped.Whenadjacentsplices ingroutedmasonryareseparatedby75mmor less, the lap lengthshallbeincreasedby30percentorthesplicemaybestaggeredatleast24bardiameterswithnoincreaseinlaplength.

7.7 StrengthDesignofSlenderWallsandShearWalls

7.7.1 DesignofSlenderWallsIn lieu of the procedure set forth in Sec 4.6, the procedures prescribed in this section,which consider theslendernessofwallsby representingeffectsofaxial forcesanddeflection incalculationofmoments,maybeusedwhentheverticalloadstressatthelocationofmaximummomentcomputedbyEq(7.7.1)doesnotexceed 0.04 f m .Thevalueof f m shallnotexceed40N/mm2.

mg

fw fA

PP + 04.0 7.7.1Slendermasonrywallsshallhaveaminimumnominalthicknessof150mm.

7.7.1.1 SlenderWallDesignProcedure

(a) Maximum Reinforcement: The reinforcement ratio shall not exceed 0.5b,where b is thebalancedsteelratio.



(b) Moment andDeflection Calculation:Allmoments and deflections of slenderwalls shall becalculatedbasedonsimplesupportconditionsattopandbottom.Forothersupportandfixityconditions, moments and deflections shall be calculated using established principles ofmechanics.

7.7.1.2 StrengthDesign

(a) Loads:FactoredloadsshallbedeterminedinaccordancewithChapter2,Loads.

(b) RequiredMoment:Requiredmomentandaxialforceshallbedeterminedatthemidheightofthewallandshallbeusedfordesign.Thefactoredmoment,Mu,atthemidheightofthewallshallbedeterminedbyEq(7.7.2).

( ) uufuwuuu PPePhwM +++= 28

2

(7.7.2)

where: u = horizontaldeflectionatmidheightunder factored load;P Deltaeffectsshallbe included

indeflectioncalculation. e = eccentricityofPu

Pu = axialloadatmidheightofwall,includingtributarywallweight.

= ufuw PP + (c)DesignStrength:Designstrengthinflexureisthenominalmomentstrength,Mn,multiplied

bythestrengthreductionfactor,andshallequalorexceedthefactoredmoment,Mu.

nu MM 7.7.3 where:

Mn= nominalmomentstrength

= ( )2adfA yse Ase = effectiveareaofsteel

= ,y

uys

fPfA +

and

a = depthofstressblockduetofactoredloads.

= bffAP

m

ysu

+85.0

Thestrengthreductionfactorforflexureshallbe0.80.(d)DesignAssumptions:The followingarethedesignassumptionsforcalculationofnominal

strength.i) Nominal strength of singly reinforced masonry wall crosssections subject to

combined flexure and axial load shall be based on applicable conditions ofequilibriumandcompatibilityofstrains.

ii) Straininreinforcementandmasonrywallsshallbeassumeddirectlyproportionaltothedistancefromtheneutralaxis.

iii) Maximum usable strain at extrememasonry compression fibre shall be assumedequalto0.003.

iv) StressinreinforcementbelowspecifiedyieldstrengthfyshallbetakenasEstimessteelstrain.Forstrainsgreater thanthatcorrespondingto fy,stress inreinforcementshallbeconsideredindependentofstrainandequaltofy.

v) Tensilestrengthofmasonrywallsshallbeneglectedinflexuralcalculationsofstrength,exceptfordeflectioncalculation.


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vi) Relationship between masonry compressive stress and masonry strain may beassumedtoberectangularasdefinedbythefollowing:

1. Masonry stress of 0.85 f m shall be assumed uniformly distributed over anequivalent compression zone bounded by edges of the crosssection and astraightlinelocatedparalleltotheneutralaxisatadistancea=0.85cfromthefibreofmaximumcompressivestrain.

2. Distancecfromfibreofmaximumstraintotheneutralaxisshallbemeasuredinadirectionperpendiculartothataxis.

7.7.1.3 DeflectionCalculation

Themidheightdeflection,s,underservice lateralandvertical loads(without loadfactors)shallbelimitedto:s0.007h 7.7.4Themidheightdeflectionshallbecomputedby:

gm

ss IE

hM485 2= whenMserMcr (7.7.5)

( )crm

crser

gm

crs IE

hMMIEhM

485

485 22 +=

when nsercr MMM



bmb bafP = 85.0 7.7.8 where

( )[ ]da symumub Efee += 85.0 (b) =0.60forshear

Theshearstrengthreductionfactormaybe0.80foranyshearwallwhen itsnominalshearstrengthexceedstheshearcorrespondingtodevelopmentofitsnominalflexuralstrengthforthefactoredloadcombination.

7.7.2.3 DesignAssumptionsforNominalStrength

(a) Nominal strength of shearwall crosssections shall be based on assumptions specified inSec7.7.1.2(d).

(b) Themaximumusablestrainemu,attheextrememasonrycompressionfibreshallnotexceed0.003.

(c) f m shallnotbelessthan7N/mm2orgreaterthan20N/mm2.

7.7.2.4 AxialStrength

ThenominalaxialstrengthofshearwallssupportingaxialloadsonlyshallbecalculatedbyEq(7.7.9)( ) sysemo AfAAfP += 85.0 (7.7.9)TheshearwallshallbedesignedfortheaxialstrengthPu,suchthat

( ) ou PP 80.0 7.7.107.7.2.5 ShearStrength

(a) Thenominalshearstrengthshallbedeterminedbytheprovisionsasspecifiedin(b)or(c)below.ThemaximumnominalshearstrengthvaluesaregiveninTable6.7.14.

Table6.7.14:MaximumNominalShearStrengthValues

VdM *

me fAn

V

0.25

1.00

72.0

48.0

* MisthemaximumbendingmomentthatoccurssimultaneouslywiththeshearloadVatthe

sectionunderconsideration.InterpolationmaybebystraightlineforM/Vdvaluesbetween0.25

and1.00.

(b) Thenominalshearstrengthofshearwallsexceptforshearwallsspecifiedin(c)belowshallbedeterminedbyEq(7.7.11).

smn VVV += (7.7.11) where:

( )mmvdm fACV = 083.0 (7.7.12) ThevalueofCdinEq(7.7.12)isgivenas:

25.0for4.2 =VdMCd

0.1for2.1 =

VdM

and


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ynmvs fAV = (7.7.13)(c) For a shearwallwhosenominal shear strength exceeds the shear corresponding to

developmentofitsnominalflexuralstrength,twoshearregionsexist.i) Forallcrosssectionswithintheregiondefinedbythebaseoftheshearwall

andaplaneatadistance Lwabove thebaseof the shearwall, thenominalshearstrengthshallbedeterminedbyEq(7.7.14)

ynmvn fAV = (7.7.14)The required shear strength for this region shallbe calculatedatadistanceLw/2 above the base of the shear wall but not to exceed onehalf storeyheight.

ii) For theother region, thenominal shear strengthof the shearwall shallbedeterminedbyEq(7.7.11).

7.7.2.6 Reinforcement

Reinforcementshallbeinaccordancewiththefollowing:

(a) MinimumreinforcementshallbeprovidedinaccordancewithSec7.8.5.1forallseismicareasusingthismethodofanalysis.

(b) Whentheshearwallfailuremodeisinflexure,thenominalflexuralstrengthoftheshearwallshallbeatleast1.8timesthecrackingmomentstrengthofafullygroutedwallor3.0timesthecrackingmomentstrengthofapartiallygroutedwallasobtainedfromEq(7.7.7).

(c) AllcontinuousreinforcementshallbeanchoredorsplicedinaccordancewithSec7.6.6.4withfs=0.5fy

(d) Verticalreinforcementshallnotbelessthan50percentofthehorizontalreinforcement.(e) SpacingofhorizontalreinforcementwithintheregiondefinedinSec7.7.2.5(c)shallnotexceed

threetimesthenominalwallthicknessor600mm,whicheverissmaller.

7.7.2.7 BoundaryMember

Boundarymembersshallbeasfollows:(a) The need for boundarymembers at boundaries of shearwall shall be determined using the

provisionssetforthin(b)or(c)below.(b) Boundary members shall be provided when the failure mode is flexure and the maximum

extreme fibre stressexceeds0.2 f m .Theboundarymembersmaybediscontinuedwhere thecalculated compressive stresses are less than 0.15 f m . Stresses may be calculated for thefactoredforcesusingalinearlyelasticmodelandgrosssectionproperties.

(c) When the failuremode is flexure,boundarymember shallbeprovided to confineall verticalreinforcementwhosecorrespondingmasonrycompressivestressexceeds0.4 f m .

(d) Theminimumlengthoftheboundarymembershallbe3timesthethicknessofthewall.(e) Boundarymembersshallbeconfinedwithminimumof10mmdiameterbarsatamaximumof

200mmspacingorequivalentwithinthegroutedcoreandwithintheregiondefinedbythebaseoftheshearwallandaplaneatadistanceLwabovethebaseoftheshearwall.

7.8 EarthquakeResistantDesign

7.8.1 GeneralAllmasonry structures constructed in the Seismic Zones 2, 3 and 4 shown in Fig 2.5.1 shall be designed inaccordancewiththeprovisionsofthisSection.



7.8.2 Loads Seismicforcesonmasonrystructuresshallbedetermined inaccordancewiththeprovisionsofSec2.5ofthisPart.

7.8.3 Materials(a) Well burnt clay bricks and concrete hollow blocks having a crushing strength not less than

12N/mm2shallbeused.(b) MortarnotleanerthanM3shallbeusedformasonryconstructions.

7.8.4 ProvisionsforSeismicZone2and3

7.8.4.1 WallReinforcement

Verticalreinforcementofatleast12mm shallbeprovidedcontinuouslyfromsupporttosupportateachcorner,ateachsideofeachopening,attheendsofwallsandatamaximumspacingof1.2mhorizontallythroughoutthewall.Horizontalreinforcementnotlessthan12mmshallbeprovided:(a) at the bottom and top ofwall openings and shall extend at least 40 bar diameters,with a

minimumof600mm,pasttheopening,(b) continuouslyatstructurallyconnectedroofandfloorlevelsandatthetopofwalls,(c) atthebottomofthewallorinthetopofthefoundationswhendowelledtothewall,(d) atmaximum spacing of 3.0m unless uniformly distributed joint reinforcement is provided.

Reinforcementatthetopandbottomofopeningswhencontinuousinthewallmaybeusedindeterminingthemaximumspacingspecifiedinitem(a)above.

7.8.4.2 StackBond

Wherestackbond isused,theminimumhorizontalreinforcementratioshallbe0.0007bt.Thisratioshallbesatisfiedbyuniformlydistributedjointreinforcementorbyhorizontalreinforcementspacednotmorethan1.2mandfullyembeddedingroutormortar.

7.8.4.3 Columns

ColumnsshallbereinforcedasspecifiedinSec7.6.6.1.

7.8.5 ProvisionsforSeismicZone4All masonry structures built in Seismic Zone 4 shall be designed and constructed in accordance withrequirementsforSeismicZone2andwiththefollowingadditionalrequirementsandlimitations. Reinforcedhollowunitstackbondconstructionwhichispartoftheseismicresistingsystemshalluseopenendunitssothatallheadjointsaremadesolid,shallusebondbeamunitstofacilitatetheflowofgroutandshallbegroutedsolid.

7.8.5.1 WallReinforcement

Reinforcedmasonrywalls shallbe reinforcedwithboth verticalandhorizontal reinforcement.Thesumoftheareasofhorizontalandverticalreinforcementshallbeatleast0.002timesthegrosscrosssectional areaof thewall and the areaof reinforcement ineitherdirection shallnotbe less than0.0007timesthegrosscrosssectionalareaofthewall.Thespacingofreinforcementshallnotexceed1.20m.Thediameterofreinforcingbarshallnotbelessthan10mmexceptthatjointreinforcementmaybe considered aspartof allof the requirements forminimum reinforcement.Reinforcementshall be continuous around wall corners and through intersections. Only reinforcement which iscontinuous in the wall or element shall be considered in computing the minimum area ofreinforcement. Reinforcement with splices conforming to Sec 7.6.6.7 shall be considered ascontinuousreinforcement.

7.8.5.2 ColumnReinforcement

Thespacingofcolumntiesshallbenotmorethan225mmforthefullheightofcolumnsstressedbytensileorcompressiveaxialoverturningforcesduetotheseismicloads,and225mmforthetopsand


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bottomsofallothercolumnsforadistanceofonesixthoftheclearcolumnheight,butnotlessthan450mmormaximumcolumndimension.Tiespacing for the remainingcolumnheightshallbenotmorethan16bardiameters,48tiediametersortheleastcolumndimension,butnotmorethan450mm.

7.8.5.3 StackBond

Wherestackbondisused,theminimumhorizontalreinforcementratioshallbe0.0015bt.Ifopenendunitsareusedandgroutedsolid,theminimumhorizontalreinforcementratioshallbe0.0007bt.

7.8.5.4 MinimumDimension

(a) BearingWalls:Thenominalthicknessofreinforcedmasonrybearingwallsshallbenotlessthan150mmexcept thatnominal100mm thick loadbearingreinforcedhollowclayunitmasonrywallsmaybeused,providednetareaunitstrengthexceeds55N/mm2,unitsarelaidinrunningbond,barsizesdonotexceed12mmwithnomorethantwobarsoronesplice inacell,andjointsareflushcut,concaveoraprotrudingVsection.

(b) Columns: The least nominal dimension of a reinforcedmasonry column shall be 375mmexceptthatiftheallowablestressesarereducedto50percentofthevaluesgiveninSec4.3,theminimumnominaldimensionshallbe250mm.

7.8.5.5 ShearWall

(a) When calculating shearordiagonal tension stresses, shearwallswhich resist seismic forcesshallbedesignedtoresist1.5timestheforcesspecifiedinChapter2,Loads.

(b) Theportionof the reinforcement required to resist shear shallbeuniformlydistributedandshallbe jointreinforcing,deformedbars,oracombinationthereof.Themaximumspacingofreinforcement in eachdirection shallbenot less than the smallerofonehalf the lengthorheightoftheelementormorethan1.20m.Joint reinforcementused inexteriorwallsand considered in thedeterminationof the shearstrengthofthemembershallconformtotherequirement"JointReinforcementforMasonry"(UBC Standard No. 2415) or "Standard Specification for Steel Wire, Plain, for ConcreteReinforcement",(ASTM,A82).Reinforcement required to resist inplane shearshallbe terminatedwitha standardhookorwithanextensionofproperembedment lengthbeyondthereinforcingattheendofthewallsection. Thehookor extensionmaybe turnedup,downorhorizontally.Provisions shallbemadenot toobstructgroutplacement.Wallreinforcementterminating incolumnsorbeamsshallbefullyanchoredintotheseelements.

(c) Multiwythegroutedmasonryshearwallsshallbedesignedwithconsiderationoftheadhesionbond strength between the grout andmasonry units.When bond strengths are not knownfromprevioustests,thebondstrengthshallbedeterminedbytest.

7.8.5.6 Hook

Thestandardhookfortieanchorageshallhaveaminimumturnof135degreesplusanextensionofat least6bardiameters,butnot less than100mmat the freeendofthebar. Wherethe tiesareplacedinthehorizontalbedjoints,thehookshallconsistofa90degreebendhavingaradiusofnotlessthan4tiediametersplusanextensionof32tiediameters.

7.8.5.7 MortarJointsBetweenMasonryandConcrete

Concreteabuttingstructuralmasonrysuchasatstartercoursesoratwallintersectionsnotdesignedastrueseparationjointsshallberoughenedtoafullamplitudeof`1.5mmandshallbebondedtothemasonryaspertherequirementsofthissectionasifitweremasonry.

7.8.6 AdditionalRequirements

7.8.6.1 OpeninginBearingWalls



(a) Topsofallopenings inastorey shallpreferablybeat the same level so thatacontinuousbandcouldbeprovidedoverthem,includingthelintelsthroughoutthebuilding.

(b) The total width of the openings shall not bemore than half of the length of the wallsbetweentheadjacentcrosswalls,exceptasprovidedin(f)below.

(c) TheopeningshallpreferablybelocatedawayfromthecornerbyacleardistanceequaltoatleastoneeighthoftheheightoftheopeningforSeismicZone2and3andonefourthoftheheightforSeismicZone4.

(d) ThehorizontaldistancebetweentwoopeningsshallnotbelessthanonefourthoftheheightoftheshorteropeningforSeismicZone2and3andonehalfoftheheightforSeismicZone4.

(e) Theverticaldistancebetweenopeningsoneabovetheothershallbenotlessthan600mm.(f) Whereopeningsdonot complywith the requirementsof (b) and (c) above, they shallbe

strengthenedinaccordancewithSec7.8.6.5.(g) Ifawindoworventilatoristobeprojectedout,theprojectionshallbeinreinforcedmasonry

orconcreteandwellanchored.(h) Ifanopeningistallsay,forthefullheightofwall,dividingthewallintotwoportions,these

portions shall be reinforcedwith horizontal reinforcement of 6mm diameter bars at notmorethan600mm intervals,oneon innerandoneonouter face,properly tied toverticalsteelatjambsandcornersorjunctionsofwallswhereused.

(i) Theuseofarches tospanover theopenings isasourceofweaknessandshallbeavoidedunlesssteeltiesareprovided.

7.8.6.2 StrengtheningArrangements

AllmasonrybuildingsshallbestrengthenedbythemethodsspecifiedinTable6.7.15.

Table6.7.15:StrengtheningofMasonryBuildingsforEarthquake

SeismicZones No.ofStorey

StrengtheningArrangementstobeProvided.

1 Upto4 a)MasonrymortarshallnotbeleanerthanM3

2 Upto2with

pitchedroof

a) Masonry mortar shall not be leaner than

M3

b) Bylintelandroofband(Sec7.8.6.3)

c) By vertical reinforcement at corners and

junctionsofwalls(Sec7.8.6.4)

d) Bracinginplanattielevelforpitchedroof*

3to4 a) Masonry mortar shall not be leaner than

M3




d) Verticalreinforcementatjambsofopenings

(Sec7.8.6.5)

e) Bracinginplanattielevelforpitchedroof*


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3 Upto4

a) Masonry mortar shall not be leaner than

M3




d) Verticalreinforcementatjambsofopenings

(Sec7.8.6.5)

e) Bracinginplanattielevelforpitchedroof* Attielevelallthetrussesandthegableendshallbeprovidedwithdiagonal

bracinginplansoastotransmitthelateralshearduetoearthquakeforcetothegablewallsactingasshearwallsattheends.

7.8.6.3 Bands

Roof band need not be provided underneath reinforced concrete or brickwork slabs resting onbearingwalls,provided theslabsarecontinuousoverpartsbetweencrumplesections, ifany, andcoverthewidthofendwallsfully.The band shall be made of reinforced concrete with f c not less than 20 N/mm2 or reinforcedbrickworkincementmortarnotleanerthan1:4.Thebandsshallbetothefullwidthofthewallandnot less than 75mm in depth and shall be reinforced as indicated in Table 6.7.16. In case ofreinforcedbrickwork,thethicknessofjointscontainingsteelbarsshallbe increasedsoastohaveaminimummortarcoverof6mmaroundthebar.Inbandsofreinforcedbrickwork,theareaofsteelprovidedshallbeequaltothatspecifiedaboveforreinforcedconcretebands.

Table6.7.16:BandReinforcement

Reinforcement

SeismicZones

PlainMildSteelBars

HighStrength

DeformedBars

Links

2 212mm,oneoneachfaceofthewall

withsuitablecover

210mm,oneoneachfaceofthewallwith

suitablecover

6mmdia,

150mmc/c

3 216mm,oneoneachfaceofthewall

withsuitablecover

212mm,oneoneachfaceofthewallwith

suitablecover

6mmdia,

150mmc/c

7.8.6.4 StrengtheningofCornerandJunctions

Verticalsteelatcornersand junctionsofwallswhichareup tooneandahalfbricks thickshallbeprovided eitherwithmild steel or high strength deformed bars as specified in Table 6.7.17. Forthickerwalls,reinforcementshallbe increasedproportionately.Thereinforcementshallbeproperlyembeddedintheplinthmasonryoffoundationsandroofslaborroofbandsoastodevelopitstensilestrengthinbondandpassingthroughthelintelbandsinallstoreys.Barsindifferentstoreysmaybeweldedorsuitablylapped.(a) Typicaldetailsofverticalsteelinbrickworkandhollowblockatcorners,Tjunctionsandjambs

ofopeningareshowninFig6.7.1andFig6.7.2.(b) Details of vertical reinforcement given in Table 6.7.17 are applicable to brickmasonry and

hollowblockmasonry.



Fig.6.7.1:Typicaldetailsofverticalreinforcementinbrickmasonry


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Fig.6.7.2:Typicaldetailsofverticalreinforcementinhollowblockmasonry

Table6.7.17:VerticalReinforcementforBrickandHollowBlockMasonry

No.ofStoreys

Storeys

DiameterofSingleBar

orEquivalentAreaofPlainMildSteelBartobe

Provided

DiameterofSingleBar

orEquivalentAreaofHighStrengthDeformedBarto

beProvided

Zone2&3

(mm)

Zone4

(mm)

Zone2&3

(mm)

Zone4

(mm)

1 nil 12 nil 10

2 Top

Bottom

nil

nil

12

16

nil

nil

10

12

3

Top

Middle

Bottom

12

12

16

12

16

16

10

10

12

10

12

12

4 Top

Third

Second

Bottom

12

12

16

16

12

16

20

25

10

10

12

12

10

12

16

20

7.8.6.5 StrengtheningofJambsofOpenings

Openings inbearingwallsshallbestrengthened,wherenecessary,byprovidingreinforcedconcretemembersorreinforcingthebrickworkaroundthemasshowninFig6.7.3.

7.8.6.6 WallsAdjoiningStructuralFraming

Wherewallsaredependentonthestructuralframeforlateralsupporttheyshallbeanchoredtothestructuralmemberswithmetaltiesorkeyedtothestructuralmembers.Horizontaltiesshallconsistof6mmdiameterUbarsspacedatamaximumof450mmoncentreandembeddedatleast250mmintothemasonryandproperlytiedtotheverticalsteelofthesamemember.



Fig.6.7.3:MinimumreinforcementinwallsandaroundopeningsinSeismicZones2,3and4

7.9 PROVISIONSFORHIGHWINDREGIONS

7.9.1 GeneralTheprovisionsofthissectionshallapplytomasonrystructureslocatedatregionswherethebasicwindspeedisgreaterthan200km/h.

7.9.2 MaterialsMaterialsformasonrystructuresshallgenerallycomplywiththeprovisionsofPart5;however,therearesomespecialrequirementsformasonryconstructioninhighwindregions,whicharegivenbelow:

(a) Burntclaybricksshallhaveacompressivestrengthnotlessthan15N/mm2,(b) Groutshallhaveaminimumcompressivestrengthof12.5N/mm2,

(c) MortarforexteriorwallsandinteriorshearwallsshallbetypeM1orM2,(d) Unburntclaymasonryunitsshallnotbeused.

7.9.3 ConstructionRequirementsMasonryconstructionshallcomplywiththeprovisionsofSec7.10.

2&34)


6400 Vol.2

7.9.4 FoundationFootingsshallhaveathicknessofnotlessthan375mmandshallbeextended450mmbelowtheundisturbedgroundsurface.Foundationstemwallshallhavethesamewidthandreinforcementasthewallitsupports.

7.9.5 DrainageWallsretainingmorethan1mofearthandenclosinginteriorspacesorfloorsbelowgradeshallhaveminimum100mmdiameterfootingdrain.Aslopeof1:50awayfromthebuildingshallbeprovidedaroundthebuilding.

7.9.6 WallConstruction

7.9.6.1 MinimumthicknessofdifferenttypesofwallshallbeasgiveninTable6.7.18.

Table6.7.18:MinimumthicknessofWallsinHighWindRegion

TypeofWall MinimumThickness(mm)

Unreinforcedgroutedbrickwall

Reinforcedexteriorbearingwall

Unreinforcedhollowandsolidmasonrywall

Interiornonbearingwall

250

200

200

150

7.9.6.2 Allwalls shallbe laterally supported at the top andbottom.Themaximumunsupportedheightofbearingwallsorothermasonrywallsshallbe3.5m.Gableendwallsmaybe4.5mhighattheirpeak.

7.9.6.3 The span of lintels over openings shall not exceed 3.5m. All lintels shall be reinforced and thereinforcementbars shallextendnot less than600mmbeyond theedgeofopeningand into lintelsupports.

7.9.6.4 Wallsshallbeadequatelyreinforced.

7.9.6.5 Anchorsbetweenwallsand floorsor roofsshallbeembedded ingroutedcellsorcavitiesandshallconformtoSec7.9.7below.

7.9.7 FloorandRoofSystemsFloorsandroofsofallmasonrystructuresshallbeadequatelyanchoredwiththewallitsupportstoresistlateralandupliftforcesduetowindspecifiedinSec2.4ofthisPart.

7.9.8 LateralForceResistance

7.9.8.1 Strapping, approved framing anchors and mechanical fasteners, bond beams and verticalreinforcement shallbe installed toprovideacontinuous tie from the roof to foundation systemasshowninFig6.7.4.Inaddition,roofandfloorsystems,masonryshearwalls,ormasonryorwoodcrosswallsshallbeprovidedforlateralstability.

7.9.8.2 Floor and roof diaphragms shall be properly connected tomasonrywalls. Gable and sloped roofmembersnotsupportedattheridgeshallbetiedbytheceilingjoistorequivalentlateraltieslocatedasclosetowheretheroofmembersbearonthewallaspracticallypossibleandnotatmorethan1.2moncenters.Collartiesshallnotbeusedfortheselateralties.

7.9.8.3 Masonry walls shall be provided around all sides of floor and roof systems in accordance withFig6.7.5.Thecumulativelengthofexteriormasonrywallsalongeachsideofthefloororroofsystems



shallbeat least20percentoftheparalleldimension.Requiredelementsshallbewithoutopeningsandshallnotbelessthat1.25minwidth.

Interiorcrosswallsatrightanglestobearingwallsshallbeprovidedwhenthelengthofthebuildingperpendiculartothespanofthefloorofroofframingexceedstwicethedistancebetweenshearwallsor10m,whicheverisgreater.

7.9.8.4 Whenrequired interiorcrosswallshallbeat least1.8m longand reinforcedwith2mmwire jointreinforcementspacednotmorethan400mmoncentre.

Fig.6.7.4:Continuoustiefromrooftofoundationofmasonrystructure

Fig.6.7.5:Masonrywallsrequiredinhighwindregions


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7.10 CONSTRUCTION

7.10.1 GeneralMasonryshallbeconstructedaccordingtotheprovisionsofthissection.

7.10.2 StorageandPreparationofConstructionMaterialsStorage,handlingandpreparationatthesiteshallconformtothefollowing:

(a) Masonrymaterialsshallbestoredinsuchawaythatatthetimeofusethematerialsarecleanandstructurallysuitablefortheintendeduse.

(b) b) Allmetalreinforcementshallbefreefromlooserustandothercoatingsthatwouldinhibitreinforcingbond.

(c) Burntclayunitsshallhavearateofabsorptionperminutenotexceedingone litrepersquaremetreat the timeof lying. In theabsorption test the surfaceof theunit shallbeheld3mmbelowthesurfaceofthewater.

(d) Burntclayunitsshallbethoroughlywettedbeforeplacing.Concretemasonryunitsshallnotbewettedunlessotherwiseapproved.

(e) Materialsshallbestoredinsuchamannerthatdeteriorationorintrusionofforeignmaterialsispreventedandatthetimeofmixingthematerialconformstotheapplicablerequirements.

(f) Themethodofmeasuringmaterialsformortarandgroutshallbesuchthatproportionsofthematerialscanbeeasilycontrolled.

(g) Mortarorgroutmixedatthejobsiteshallbemixedforaperiodoftimenotlessthan3minutesormorethan10minutes inamechanicalmixerwiththeamountofwaterrequiredtoprovidethedesiredworkability.Handmixingofsmallamountsofmortar ispermitted.Mortarmayberetempered.Mortarorgroutwhichhashardenedorstiffenedduetohydrationofthecementshallnotbeused,but undernocaseshallmortarbeused twoandonehalfhours,norgroutused one and onehalf hours, after the initial mixing water has been added to the dryingredientsatthejobsite.

7.10.3 PlacingMasonryUnits(a) Themortarshallbesufficientlyplasticandunitsshallbeplacedwithsufficientpressureto

extrudemortar from the jointandproducea tight joint.Deep furrowingwhichproducesvoidsshallnotbeused.Theinitialbedjointthicknessshallnotbelessthan5mmormorethan25mm;subsequentbedjointsshallbenotlessthan5mmormorethan15mminthickness.

(b) Allsurfacesincontactwithmortarorgroutshallbecleanandfreeofdeleteriousmaterials.(c) Solidmasonryunitsshallhavefullheadandbedjoints.(d) Allheadandbedjointsshallbefilledsolidlywithmortarforadistancefromthefaceofthe

unitnotlessthanthethicknessoftheshell.Head jointsofopenendunitswithbeveledendsneednotbemortared.Thebeveledendsshallformagroutkeywhichpermitsgroutwithin16mmofthefaceoftheunit.Theunitsshallbetightlybuttedtopreventleakageofgrout.

7.10.4 VerticalityandAlignmentAllmasonryshallbebuilttrueandplumbwithinthetolerancesprescribedbelow.Careshallbetakentokeeptheperpendsproperlyaligned.

(a) Deviationfromverticalwithinastoreyshallnotexceed6mmper3mheight.(b) Deviation in verticality in total height of anywall of a buildingmore than one storey in

heightshallnotexceed12mm.(c) Deviationfrompositionshownonplanofanybrickworkshallnotexceed12mm.(d) Relative displacement between load bearingwalls in adjacent storeys intended to be in

verticalalignmentshallnotexceed6mm.



(e) Deviationofbedjointfromhorizontalinalengthof12mshallnotexceed6mmsubjecttoamaximumdeviationof12mm.

(f) Deviation from the specified thicknessof bed joints, cross joints and perpends shall notexceedonefifthofthespecifiedthickness.

7.10.5 ReinforcementPlacingReinforcing details shall conform to the requirements of Sec 4.6.6.Metal reinforcement shall be located inaccordancewith the plans and specifications.Reinforcement shall be secured against displacement prior togroutingbywirepositionersorothersuitabledevicesatintervalsnotexceeding20bardiameters.Tolerancesfortheplacementofsteelinwallsandflexuralelementsshallbe12mmford200mm,25mmfor200mmd600mmand30mmford>600mm.Toleranceforlongitudinallocationofreinforcementshallbe50mm.

7.10.6 GroutedMasonryGroutedmasonryshallbeconstructedinsuchamannerthatallelementsacttogetherasastructuralelement.Space tobe filledwithgrout shallbe cleanand shallnot containany foreignmaterials.Groutmaterialsandwatercontentshallbecontrolledtoprovideadequateworkabilityandshallbemixedthoroughly.Thegroutingofanysectionofwallshallbecompletedinonedaywithnointerruptionsgreaterthanonehour.SizeandheightlimitationsofthegroutspaceorcellshallnotbelessthanthoseshowninTable6.7.19.HighergroutpoursorsmallercavitywidthsorcellsizethanshowninTable6.7.19maybeusedwhenapproved,ifitcanbedemonstratedthatgroutspacesareproperlyfilled.Cleanoutsarerequiredforallgroutpoursover1.5minheight.Whenrequired,cleanoutsshallbeprovidedinthebottomcourseateveryverticalbarbutshallnotbespacedmorethan800mmoncentreforsolidlygroutedmasonry. When cleanouts are required, they shall be sealed after inspection and before grouting. Whencleanoutsarenotprovided,specialprovisionsmustbemadetokeepthebottomandsidesofthegroutspaces,aswellastheminimumtotalclearareaasrequiredbyTable6.7.19,cleanandclearpriortogrouting.

Table6.7.19:GroutingLimitations

GroutType

GroutpourMaximum

Height(m)

MinimumDimensionsoftheTotalClearAreaswithinGroutSpacesandCells

MultiwytheMasonry(mm )

HollowUnitMasonry

(mm)

Fine

Fine

Fine

Fine

Fine

0.30

1.50

2.40

3.65

7.30

20

40

40

40

50

40 5040 5040 7545 7575 75

Coarse

Coarse

Coarse

Coarse

Coarse

0.30

1.50

2.40

3.65

7.30

40

50

50

60

75

40 7560 7575 7575 7575 100

7.10.7 Chases,RecessesandHoles(a) Chases,recessesandholesmaybepermitted inmasonryprovidedeithertheyareconsidered

in thestructuraldesignor theyarenotcut intowallsmadeofholloworperforatedunits,orverticalchasesareplannedinsteadofhorizontalchases.


6404 Vol.2

(b) Depthof vertical andhorizontal chases in loadbearingwalls shallnotexceedonethirdandonesixthofthewallthicknessrespectively.

(c) Vertical chases shallnotbe closer than 2m in any stretchofwall and shallnotbe locatedwithin350mmofanopeningorwithin230mmofacrosswallthatservesasstiffeningwallforstability.Widthofaverticalchaseshallnotexceedthethicknessofwallinwhichitoccurs.

(d) Horizontal chases shall be located in the upper or lowermiddle third height of wall at adistance not less than 600mm from lateral support.No horizontal chase shall exceed onemetre in lengthandthereshallnotbemorethan2chases inanyonewall.Horizontalchasesshallhaveminimummutualseparationdistanceof500mm.Sumof lengthsofallchasesandrecessesinanyhorizontalplaneshallnotexceedonefourththelengthofthewall.

(e) Lintelshallnotbeusedtosupportmasonrydirectlyabovearecessoraholewiderthan300mm.No lintelhowever, isnecessary incaseofacircularrecessorholeexceeding300mm indiameterprovidedupperhalfoftherecessorholeisbuiltasasemicirculararchofadequatethickness and there is adequate length ofmasonry on the sides of openings to resist thehorizontalthrust.

(f) Re

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