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Transcript of Indian Standard_ CODE OF PRACTICE FOR DESIGN LOADS (OTHER THAN EARTHQUAKE) FOR BUILDINGS AND...
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12/19/2014 IndianStandard:CODEOFPRACTICEFORDESIGNLOADS(OTHERTHANEARTHQUAKE)FORBUILDINGSANDSTRUCTURESPART5S
https://law.resource.org/pub/in/bis/S03/is.875.5.1987.html 1/18
PREAMBLE(NOTPARTOFTHESTANDARD)
Inordertopromotepubliceducationandpublicsafety,equaljusticeforall,abetterinformedcitizenry,theruleoflaw,worldtradeandworldpeace,thislegaldocumentisherebymadeavailableonanoncommercialbasis,asitistherightofallhumanstoknowandspeakthelawsthatgovernthem.
ENDOFPREAMBLE(NOTPARTOFTHESTANDARD)
IS:875(Part5)1987
(Reaffirmed2008)
IndianStandardCODEOFPRACTICEFORDESIGNLOADS(OTHERTHANEARTHQUAKE)FORBUILDINGSANDSTRUCTURESPART5SPECIALLOADSANDLOADCOMBINATIONS
(SecondRevision)
SeventhReprintJANUARY2011(IncludingAmendmentNo.1)
UDC624.042:006.76
Copyright1988
BUREAUOFINDIANSTANDARDSMANAKBHAVAN,9BAHADURSHAHZAFARMARG
NEWDELHI110002
Gr5
July1988
IndianStandardCODEOFPRACTICEFORDESIGNLOADS(OTHERTHANEARTHQUAKE)FORBUILDINGS
ANDSTRUCTURES
PART5SPECIALLOADSANDLOADCOMBINATIONS
(SecondRevision)
StructuralSafetySectionalCommittee,BDC37
Chairman Representing
BrigDrL.V.Ramakrishna EngineerinChiefsBranch,ArmyHeadquarters,NewDelhi
Members
DrK.G.Bhatia BharatHeavyElectricalsLimited,CorporateResearch&DevelopmentDivision,Hyderabad
ShriM.S.Bhatia Inpersonalcapacity(A2/36,SafdarjangEnclave,NewDelhi)
ShriN.K.Bhattacharya EngineerinChiefsBranch,ArmyHeadquarters,NewDelhi
ShriS.K.Malhotra(Alternate)
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DrS.C.Chakrabarti CentralBuildingResearchInstitute(CSIR),Roorkee
ShriA.Datta(Alternate)
ChiefEngineer(NDZ)II CentralPublicWorksDepartment,NewDelhi
SuperintendingSurveyorofWorks(NDZ)II(Alternate)
DrP.Dayaratnam IndianInstituteofTechnology,Kanpur
DrA.S.R.Sai(Alternate)
DeputyMunicipalCommissioner(Engg)
MunicipalCorporationofGreaterBombay,Bombay
CityEngineer(Alternate)
Director(CMDDI) CentralWaterCommission,NewDelhi
DeputyDirector(CMDDI)(Alternate)
MajGenA.M.Goglekar InstitutionofEngineers(India),Calcutta
ProfD.N.Trikha(Alternate)
Copyright1988
BUREAUOFINDIANSTANDARDS
ThispublicationisprotectedundertheIndianCopyrightAct(XIVof1957)andreproductioninwholeorinpartbyanymeansexceptwithwrittenpermissionofthepublishershallbedeemedtobeaninfringementofcopyrightunderthesaidAct.
Members Representing
ShriA.C.Gupta NationalThermalPowerCorporationLtd,NewDelhi
ShriP.SenGupta StewartsandLloydsofIndiaLtd,Calcutta
ShriM.M.Ghosh(Alternate)
ShriG.B.Jahagirdar NationalIndustrialDevelopmentCorporationLtd,NewDelhi
JointDirectorStandards(B&S),CB MinistryofRailways
ShriS.P.Joshi TataConsultingEngineers,NewDelhi
ShriA.P.Mull(Alternate)
ShriS.R.Kulkarni M.N.Dastur&Co,Calcutta
ShriS.N.Pal(Alternate)
ShriH.N.Mishra ForestResearchInstituteandColleges,DehraDun
ShriR.K.Punhani(Alternate)
ShriT.K.D.Munshi EngineersIndiaLtd,NewDelhi
DrC.Rajkumar NationalCouncilforCement&BuildingMaterials,NewDelhi
DrM.N.KeshwaRao StructuralEngineeringResearchCentre(CSIR),Madras
ShriM.V.Dharaneepathy(Alternate)
ShriT.N.SubbaRao GammonIndiaLtd,Bombay
DrS.V.Lonkar(Alternate)
ShriP.K.Ray IndianEngineeringAssociation,Calcutta
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ShriP.K.Mukherjee(Alternate)
ShriS.Seetharaman MinistryofSurfaceTransport(RoadsWing),NewDelhi
ShriS.P.Chakraborty(Alternate)
ShriM.C.Sharma IndianMeteorologicalDepartment,NewDelhi
ShriK.S.Srinivasan NationalBuildingsOrganization,NewDelhi
ShriA.K.Lal(Alternate)
ShriSushilKumar NationalBuildingConstructionCorporationLtd,NewDelhi
ShriG.Raman,Director(CivEngg) DirectorGeneral,BIS(ExofficioMember)
SecretaryShriB.R.Narayanappa
DeputyDirector(CivEngg),BIS
(continuedonpage18)
IndianStandardCODEOFPRACTICEFORDESIGNLOADS(OTHERTHANEARTHQUAKE)FORBUILDINGS
ANDSTRUCTURES
PART5SPECIALLOADSANDLOADCOMBINATIONS
(SecondRevision)
0.FOREWORD
0.1
ThisIndianStandard(Part5)(SecondRevision)wasadoptedbytheBureauofIndianStandardson31August1987,afterthedraftfinalizedbytheStructuralSafetySectionalCommitteehadbeenapprovedbytheCivilEngineeringDivisionCouncil.
0.2
Abuildinghastoperformmanyfunctionssatisfacorily.Amongstthesefunctionsaretheutilityofthebuildingfortheintendeduseandoccupancy,structuralsafety,firesafetyandcompliancewithhygienic,sanitation,ventilationanddaylightstandards.Thedesignofthebuildingisdependentupontheminimumrequirementsprescribedforeachoftheabovefunctions.Theminimumrequirementspertainingtothestructuralsafetyofbuildingsarebeingcoveredinthiscodebywayoflayingdownminimumdesignloadswhichhavetobeassumedfordeadloads,imposedloads,snowloadsandotherexternalloads,thestructurewouldberequiredtobear.Strictconformitytoloadingstandardsrecommendedinthiscode,itishoped,willnotonlyensurethestructuralsafetyofthebuildingswhicharebeingdesignedandconstructedinthecountryandtherebyreducethehazardstolifeandpropertycausedbyunsafestructures,butalsoeliminatethewastagecausedbyassumingunnecessarilyheavyloadings.Notwithstandingwhatisstatedregardingthestructuralsafetyofbuildings,theapplicationoftheprovisionsshouldbecarriedoutbycompetentandresponsiblestructuraldesignerwhowouldsatisfyhimselfthatthestructuredesignedinaccordancewiththiscodemeetsthedesiredperformancerequirementswhenthesameiscarriedoutaccordingtospecifications.
0.3
Thisstandardcodeofpracticewasfirstpublishedin1957fortheguidanceofcivilengineers,
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designersandarchitectsassociatedwithplanninganddesignofbuildings.Itincludedtheprovisionsforbasicdesign
loads(deadloads,liveloadswindloadsandseismicloads)tobeassumedinthedesignofbuildings.Initsfirstrevisionin1964,thewindpressureprovisionsweremodifiedonthebasisofstudiesofwindphenomenonanditseffectsonstructures,undertakenbythespecialcommitteeinconsultationwiththeIndianMeteorologicalDepartment.Inadditiontothis,newclausesonwindloadsforbutterflytypestructureswereincludedwindpressurecoefficientsforsheetedroofsbothcurvedandslopingweremodifiedseismicloadprovisionsweredeleted(separatecodehavingbeenprepared)andmetricsystemofweightsandmeasurementswasadopted.
0.3.1
Withtheincreasedadoptionofthecode,anumberofcommentswerereceivedontheprovisionsonliveloadvaluesadoptedfordifferentoccupancies.SimultaneouslyliveloadsurveyshavebeencarriedoutinAmerica,Canadaandothercountriestoarriveatrealisticliveloadsbasedonactualdeterminationofloading(movableandimmovable)indifferentoccupancies.Keepingthisinviewandotherdevelopmentsinthefieldofwindengineering,thecommitteeresponsibleforthepreparationofthestandarddecidedtopreparesecondrevisioninthefollowingfiveparts:
Part1Deadloads
Part2Imposedloads
Part3Windloads
Part4Snowloads
Part5Specialloadsandloadcombinations.
Earthquakeloadiscoveredinaseparatestandard,namelyIS:18931984*whichshouldbeconsideredalongwiththeaboveloads.
0.3.2
Thiscode(Part5)dealswithloadsandloadeffects(otherthanthosecoveredinParts1to4,andseismicloads)duetotemperaturechanges,internallygeneratingstresses(duetocreep,shrinkage,differentialsettlement,etc)inthebuildinganditscomponents,soilandhydrostaticpressure,accidentalloads,etc.Thispartalsoincludesguidance,onloadcombinations.
*Criteriaforearthquakeresistantdesignofstructures(thirdrevision).
0.4
ThecodehastakenintoaccounttheprevailingpracticesinregardtoloadingstandardsfollowedinthiscountrybythevariousmunicipalauthoritiesandhasalsotakennoteofthedevelopmentsinanumberofcountriesabroadInthepreparationofthiscode,thefollowing,nationalstandardshavebeenexamined:
a. NationalBuildingCodeofCanada(1977)SupplementNo:4.CanadianStructuralDesignManual.
b. DS4101983Codeofpracticeforloadsforthedesignofstructures.DanishStandardsInstitution.
c. NZS42031976NewZealandStandardGeneralstructuraldesignanddesignloadingforbuilding.StandardsAssociationofNewZealand.
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d. ANSIA58.11982AmericanStandardBuildingcoderequirementsforminimumdesignloadsinbuildingsandotherstructures.
1.SCOPE
1.1
Thiscode(Part5)dealswithloadsandloadeffectsduetotemperaturechanges,soilandhydrostaticpressures,internallygeneratingstresses,(duetocreep,shrinkage,differentialsettlement,etc),accidentalloadsetc,tobeconsideredinthedesignofbuildingsasappropriate.Thispartalsoincludesguidanceonloadcombinations.Thenatureofloadstobeconsideredforaparticularsituationistobebasedonengineeringjudgement.
2.TEMPERATUREEFFECTS
2.1
Expansionandcontractionduetochangesintemperatureofthematerialsofastructureshallbeconsideredindesign.Provisionshallbemadeeithertorelievethestressbyprovisionofexpansion/contractionjointsinaccordancewithIS:34141968*ordesignthestructuretocarryadditionalstressesduetotemperatureeffectsasappropriatetotheproblem.
2.1.1
Thetemperaturerangevariesfordifferentregionsandunderdifferentdiurnalandseasonalconditions.TheabsolutemaximumandminimumtemperaturewhichmaybeexpectedindifferentlocalitiesinthecountryareindicatedinFig.1and2respectively.Thesefiguresmaybeusedforguidanceinassessingthemaximumvariationsoftemperature.
2.1.2
ThetemperaturesindicatedinFig.1and2aretheairtemperaturesintheshade.Therangeofvariationintemperatureofthebuildingmaterialsmaybeappreciablygreaterorlessthanthevariationofairtemperatureandisinfluencedbytheconditionofexposureandtherateatwhichthematerialscomposingthestructureabsorborradiateheat.Thisdifferenceintemperaturevariationsofthematerialandairshouldbegivendueconsideration.
2.1.3
Thestructuralanalysismusttakeintoaccount:(a)changesofthemean(throughthesection)temperatureinrelationtotheinitialtemperature(st),and(b)thetemperaturegradientthroughthesection.
*Codeofpracticefordesignandinstallationofjointsinbuildings.
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Fig.1ChartShowingHighestMaximumTemperature
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Fig.2ChartShowingLowestMinimumTemperature
2.1.3.1
Itshouldbeborneinmindthatthechangesofmeantemperatureinrelationtotheinitialareliabletodifferasbetweenonestructuralelementandanotherinbuildingsorstructures,asforexample,betweentheexternalwallsandtheinternalelementsofabuilding.Thedistributionoftemperaturethroughsectionofsingleleafstructuralelementsmaybeassumedlinearforthepurposeofanalysis.
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2.1.3.2
Theeffectofmeantemperaturechangest1,andt2,andthetemperaturegradientsv1andv2in
thehotandcoldseasonsforsingleleafstructuralelementsshallbeevaluatedonthebasisofanalyticalprinciples.
Note1Forportionsofthestructurebelowgroundlevel,thevariationoftemperatureisgenerallyinsignificant.However,duringtheperiodofconstructionwhentheportionsofthestructureareexposedtoweatherelements,adequateprovisionshouldbemadetoencounteradverseeffects,ifany.
Note2Ifitcanbeshownbyengineeringprinciples,orifitisknownfromexperience,thatneglectofsomeoralltheeffectsoftemperaturedonotaffectthestructuralsafetyandserviceability,theyneednotbeconsideredindesign,
3.HYDROSTATICANDSOILPRESSURE
3.1
Inthedesignofstructuresorpartsofstructuresbelowgroundlevel,suchasretainingwallsandotherwallsinbasementfloors,thepressureexertedbysoilorwaterorbothshallbedulyaccountedforonthebasisofestablishedtheories.Dueallowanceshallbemadeforpossiblesurchargefromstationaryormovingloads.Whenaportionorwholeofthesoilisbelowthefreewatersurface,thelateralearthpressureshallbeevaluatedforweightofsoildiminishedbybuoyancyandthefullhydrostaticpressure.
3.1.1
Allfoundationslabsandotherfootingssubjectedtowaterpressureshallbedesignedtoresistauniformlydistributedupliftequaltothefullhydrostaticpressure.Checkingofoverturningoffoundationundersubmergedconditionshallbedoneconsideringbuoyantweightoffoundation.
3.2
Whiledeterminingthelateralsoilpressureoncolumnlikestructuralmembers,suchaspillarswhichrestinslopingsoils,thewidthofthemembershallbetakenasfollows(seeFig.3):
ActualWidthofMember RatioofEffectiveWidthtoActualWidth
Lessthan05m 30
Beyond05mandupto1m 30to20
Beyond1m 20
Therelievingpressureofsoilinfrontofthestructuralmemberconcernedmaygenerallynotbetakenintoaccount.
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Fig.3SketchShowingEffectiveWidthOfPillarForCalculatingSoilPressure
3.3
Safeguardingofstructuresandstructuralmembersagainstoverturningandhorizontalslidingshallbeverified.Imposedloadshavingfavourableeffectshallbedisregardedforthepurpose.Dueconsiderationshallbegiventothepossibilityofsoilbeingpermanentlyortemporarilyremoved.
4.FATIGUE
4.1
GeneralFatiguecracksareusuallyinitiatedatpointsofhighstressconcentration.Thesestressconcentrationsmaybecausedbyorassociatedwithholes(suchasboltorrivetholesinsteelstructures),weldsincludingstrayorfusionsinsteelstructures,defectsinmaterials,andlocalandgeneralchangesingeometryofmembers.Thecracksusuallypropagateiftheloadingiscyclicandrepetitive.
Wherethereissuchcyclicandrepetitiveloading,suddenchangesofshapeofamemberorpartofamember,speciallyinregionsoftensilestressand/orlocalsecondarybending,shallbeavoided.Suitablestepsshallbetakentoavoidcriticalvibrationsduetowindandothercauses
4.2
Wherenecessary,permissiblestressesshallbereducedtoallowfortheeffectsoffatigue.Allowanceforfatigueshallbemadeforcombinationsofstressesduetodeadloadandimposedload.Stressesduetowindandearthquakesmaybeignoredwhenfatigueisbeingconsideredunlessotherwisespecifiedintherelevantcodesofpractice.
Eachelementofthestructureshallbedesignedforthenumberofstresscyclesofeachmagnitudetowhichitisestimatedthattheelementisliabletobesubjectedduringtheexpectedlifeofthestructure.Thenumberofcyclesofeachmagnitudeshallbeestimatedinthelightofavailabledataregardingtheprobablefrequencyofoccurrenceofeachtypeofloading.
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NoteApartfromthegeneralobservationsmadehereinthecodeisunabletoprovideanypreciseguidanceinestimatingtheprobablisticbehaviourandresponseofstructuresofvarioustypesarisingoutofrepetitiveloadingapproachingfatigueconditionsinstructuralmembers,joints,materials,etc.
5.STRUCTURALSAFETYDURINGCONSTRUCTION
5.1
Allloadsrequiredtobecarriedbythestructuresoranypartofitduetostorageorpositioningofconstructionmaterialsanderectionequipmentincludingallloadsduetooperationofsuchequipment,shallbeconsideredaserectionloads.Properprovisionshallbemade,includingtemporarybracingstotakecareofallstressesduetoerectionloads.Thestructureasawholeandallpartsofstructureinconjunctionwiththetemporarybracingsshallbecapableofsustainingtheseerectionloadswithoutexceedingthepermissiblestressesspecifiedinrespectivecodesofpractice.Deadload,windloadandsuchpartsofimposedloadaswouldbeimposedonthestructureduringtheperiodoferectionshallbetakenasactingtogetherwitherectionloads.
6.ACCIDENTALLOADS
6.0
GeneralTheoccurrenceofaccidentalloadswithasignificantvalue,isunlikelyonagivenstructureovertheperiodoftimeunderconsideration,andalsoinmostcasesisofshortduration.Theoccurrenceofanaccidentalloadcouldinmanycasesbeexpectedtocausesevereconsequencesunlessspecialmeasuresaretaken:
Theaccidentalloadsarisingoutofhumanactionincludethefollowing:
a. Impactsandcollisions,
b. Explosions,and
c. Fire.
Characteristicoftheabovestatedloadsarethattheyarenotaconsequenceofnormaluseandthattheyareundesired,andthatextensiveeffortsaremadetoavoidthem.Asaresult,theprobabilityofoccurrenceofanaccidentalloadissmallwhereastheconsequencesmaybesevere.
Thecausesofaccidentalloadsmaybe:
a. inadequatesafetyofequipment(duetopoordesignorpoormaintenance)and
b. wrongoperation(duetoinsufficientteachingortraining,indisposition,negligenceorunfavourableexternalcircumstances).
Inmostcases,accidentalloadsonlydevelopunderacombinationofseveralunfavourableoccurrence.Inpracticalapplications,itmaybenecessarytoneglectthemostunlikelyloads.Theprobabilityofoccurrenceofaccidentalloadswhichareneglectedmaydifferfordifferentconsequencesofapossiblefailure.Adatabaseforadetailedcalculationoftheprobabilitywillseldombeavailable.
NoteDeterminationofAccidentalLoadsTypesandmagnitudeofaccidentalloadsshouldpreferablybebasedonariskanalysis.Theanalysisshouldconsiderallfactorsinfluencingthemagnitudeoftheaction,includingpreventivemeasuresforaccidental
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situations.Generally,onlytheprincipalloadbearingsystemneedbedesignedforrelevantultimatelimitstates.
6.1ImpactsandCollisions
6.1.1
GeneralDuringanimpact,thekineticimpactenergyhastobeabsorbedbythevehiclehittingthestructureandbythestructureitself.Inanaccurateanalysis,theprobabilityofoccurrenceofanimpactwithacertainenergyandthedeformationcharacteristicsoftheobjecthittingthestructureandthestructureitselfattheactualplacemustbeconsidered.Impactenergiesfordroppedobjectsshouldbebasedontheactualloadingcapacityandliftingheight.
Commonsourcesofimpactare:
a. vehicles
b. droppedobjectsfromcranes,forklifts,etc
c. cranesoutofcontrol,cranefailuresand
d. flyingfragments.
Thecodalrequirementsregardingimpactfromvehiclesandcranesaregivenin6.1.2and6.1.3.
6.1.2
CollisionsBetweenVehiclesandStructuralElementsInroadtraffic,therequirementthatastructureshallbeabletoresistcollisionmaybeassumedtobefulfilledifitisdemonstratedthatthestructuralelementisabletostopafictitiousvehicle,asdescribedinthefollowing.Itisassumedthatthevehiclestrikesthestructuralelementatheightof12minanypossibledirectionandataspeedof10m/s(36km/h).
Thefictitiousvehicleshallbeconsideredtoconsistoftwomassesm1andm2whichduring
compressionofthevehicleproduceanimpactforceincreasinguniformlyfromzero,correspondingtotherigiditiesC1andC2.Itisassumedthatthemassm1isbreakedcompletelybeforethebrakingofmass
m2begins.
Thefollowingnumericalvaluesshouldbeused:
m1=400kg,C1=10000kNpermthevehicleiscompressed.
m2=12000kg,C2=300kNpermthevehicleiscompressed.
NoteThedescribedfictitiouscollisioncorrespondsinthecaseofanonelasticstructuralelementtoamaximumstaticforceof630kNforthemassm1and600kNfor
themassm2irrespectiveoftheelasticity.Itwill,therefore,beonthesafesidetoassume
thestaticforcetobe630kN.
Inaddition,brakingofthemassm1willresultinanimpactwave,theeffectofwhichwilldepend
toagreatextentonthekindofstructuralelementconcerned.Consequently,itwillnotalwaysbesufficienttodesignforthestaticforce.
6.1.3
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SafetyRailingsWithregardtosafetyrailingsputuptoprotectstructuresagainstcollisionduetoroadtraffic,itshouldbeshownthattherailingsareabletoresistonimpactasdescribedin6.1.2.
NoteWhenavehiclecollideswithsafetyrailings,thekineticenergyofthevehiclewillbeabsorbedinpartbythedeformationoftherailingsand,inpartbythedeformationofthevehicle.Thepartofthekineticenergywhichtherailingsshouldbeabletoabsorbwithoutbreakingdownmaybedeterminedonthebasisoftheassumedrigidityofthevehicleduringthecompression.
6.1.4
CraneImpactLoadonBufferStopThebasichorizontalloadPy(tonnes),actingalongthe
cranetrackproducedbyimpactofthecraneonthebufferstop,iscalculatedbythefollowingformula:
Py=MV2/F
where
V = speedatwhichthecraneistravellingatthemomentofimpact(assumedequaltohalfthenominalvalue)(m/s)
F = maximumshorteningofthebuffer,assumedequalto01mforlightduty,mediumdutyandheavydutycraneswithflexibleloadsuspensionandloadingcapacitynotexceeding50t,and02mineveryothercranesand
M = thereducedcranemass(t.s2/m)andisobtainedbytheformula:
where
g = accelerationduetogravity(981m/s2)
Ph = cranebridgeweight(t)
Pt = crabweight(t)
k = acoefficient,assumedequaltozeroforcraneswithflexibleloadsuspensionandequaltooneforcraneswithrigidsuspension
Q = craneloadingcapacity(t)
Lk = cranespan(m)and
l = nearnessofcrab(m).
6.2Explosions
6.2.1
GeneralExplosionsmaycauseimpulsiveloadingonastructure.Thefollowingtypesofexplosionsareparticularlyrelevant:
a. Internalgasexplosionswhichmaybecausedbyleakageofgaspiping(includingpipingoutsidetheroom),evaporationfromvolatileliquidsorunintentionalevaporationfromsurfacematerial(forexample,fire)
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b. Internaldustexplosions
c. Boilerfailure
d. Externalgascloudexplosionsand
e. Externalexplosionsofhighexplosives(TNT,dynamite).
Thecodalrequirementregardinginternalgasexplosionsisgivenin6.2.2.
6.2.2
ExplosionEffectinClosedRoomsGasexplosionmaybecaused,forexample,byleaksingaspipes(inclusiveofpipesoutsidetheroom),evaporationfromvolatileliquidsorunintentionalevaporationofgasfromwallsheathings(forexample,causedbyfire).
Note1Theeffectofexplosionsdependsontheexplodingmedium,theconcentrationoftheexplosion,theshapeoftheroom,possibilitiesofventilationoftheexplosion,andtheductilityanddynamicpropertiesofthestructure.Inroomswithlittlepossibilityforreliefofthepressurefromtheexplosion,verylargepressuresmayoccur.
Internaloverpressurefromaninternalgasexplosioninroomsofsizescomparabletoresidentialroomsandwithventilationareasconsistingofwindowglassbreakingata
pressureof4kN/m2(34mmmachinemadeglass)maybecalculatedfromthefollowingmethod:
a. TheoverpressureisassumedtodependonafactorA/V,whereAisthetotalwindow
areainm2,Visthevolumeinm2oftheroomconsidered.
b. Theinternalpressureisassumedtoactsimultaneouslyuponallwallsandfloorsinoneclosedroom.
c. Theactionqomaybetakenasstaticaction.
Ifaccountistakenofthetimecurveofaction,thefollowing(Fig.4)schematiccorrespondencebetweenpressureandtimeisassumed,wheret1isthetimefromthestart
ofcombustionuntilmaximumpressureisreached,andt2isthetimefrommaximum
pressuretotheendofcombustion.Fort1andt2,themostunfavourablevaluesshouldbe
choseninrelationtothedynamicpropertiesofthestructures.However,thevaluesshouldbechosenwithintheintervalsasgiveninFig.5.
Note2Figure4isbasedontestswithgasexplosionsinroomcorrespondingtoordinaryresidentialflatsandshould,therefore,notbeappliedtoconsiderablydifferentconditions.Thefigurecorrespondstoanexplosioncausedbytowngasanditmighttherefore,besomewhatonthesafesideinroomswherethereisonlythepossibilityofgaseswithalowerrateofcombustion.
Thepressuremaybeappliedsolelyinoneroomorinmoreroomsatthesametime.Inthelattercase,allroomsareincorporatedinthevolumeV.Onlywindowsorothersimilarlyweakandlightweightstructuralelementsmaybetakentobeventilationareaseventhroughcertainlimitedstructuralpartsbreakatpressureslessthanqo.
Figure4isgivenpurelyasguideandprobabilityofoccurrenceofanexplosionshouldbecheckedineachcaseusingappropriatevalues.
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6.3VerticalLoadonAirRaidShelters
6.3.1
CharacteristicValuesAsregardsbuildingsinwhichtheindividualfloorsareacteduponbya
totalcharacteristicimposedactionofupto50kN/m2,verticalactionsonairraidsheltersgenerallylocatedbelowgroundlevel,forexample,basement,etc,shouldbeconsideredtohavethefollowingcharacteristicvalues:
a) Buildingswithupto2storeys 28kN/m2
b) Buildingswith3to4storeys 34kN/m2
c) Buildingswithmorethan4storeys 41kN/m2
d) Buildingsofparticularlystableconstructionirrespectiveofthenumberofstoreys 28kN/m2
Inthecaseofbuildingswithfloorsthatareacteduponbyacharacteristicimposedactionlarger
than50kN/m2,theabovevaluesshouldbeincreasedbythedifferencebetweentheaverageimposed
actiononallstoreysabovetheoneconcernedand50kN/m2.
Note1Bystoreysitisunderstood,everyutilizablestoreyabovetheshelter.
Note2Bybuildingsofaparticularstableconstructionitisunderstood,buildingsinwhichtheloadbearingstructuresaremadefromreinforcedinsituconcrete.
Fig.4SketchShowingRelationBetweenPressureandTime
Fig.5SketchShowingTimeIntervalAndPressure
6.4Fire
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6.4.1
GeneralPossibleextraordinaryloadsduringafiremaybeconsideredasaccidentalactions.Examplesareloadsfrompeoplealongescaperoutesandloadsonanotherstructurefromstructurefailingbecauseofafire.
6.4.2
ThermalEffectDuringFireThethermaleffectduringfiremaybedeterminedfromoneofthefollowingmethods:
a. Timetemperaturecurveandtherequiredfireresistance(minutes),or
b. Energybalancemethod.
Ifthethermaleffectduringfireisdeterminedfromenergybalancemethod,thefireloadistakentobe:
q=12tb
where
q = fireaction(KJperm2floor),and
tb = requiredfireresistance(minutes)(seeIS:16421960*).
NoteThefireactionisdefinedasthetotalquantityofheatproducedbycompletecombustionofallcombustiblematerialinthefirecompartment,inclusiveofstoredgoodsandequipmenttogetherwithbuildingstructuresandbuildingmaterials.
7.OTHERLOADS
7.1
Otherloadsnotincludedinthepresentcodesuchasspecialloadsduetotechnicalprocess,moistureandshrinkageeffects,etc,shouldbetakenintoaccountwherestipulatedbybuildingdesigncodesorestablishedinaccordancewiththeperformancerequirementofthestructure.
8.LOADCOMBINATIONS
8.0
GeneralAjudiciouscombinationoftheloads(specifiedinParts1to4ofthisstandardandearthquake),keepinginviewtheprobabilityof:
a. theiractingtogether,and
b. theirdispositioninrelationtootherloadsandseverityofstressesordeformationscausedbycombinationsofthevariousloadsisnecessarytoensuretherequiredsafetyandeconomyinthedesignofastructure.
*Codeofpracticeforsafetyofbuildings(general):Materialsanddetailsofconstruction.
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8.1
LoadCombinationsKeepingtheaspectspecifiedin8.0,thevariousloadsshould,therefore,becombinedinaccordancewiththestipulationsintherelevantdesigncodes.Intheabsenceofsuchrecommendations,thefollowingloadingcombinations,whichevercombinationproducesthemostunfavourableeffectinthebuilding,foundationorstructuralmemberconcernedmaybeadopted(asageneralguidance).Itshouldalsoberecognizedinloadcombinationsthatthesimultaneousoccurrenceofmaximumvaluesofwind,earthquake,imposedandsnowloadsisnotlikely.
a. DL
b. DL+IL
c. DL+WL
d. DL+EL
e. DL+TL
f. DL+IL+WL
g. DL+IL+EL
h. DL+IL+TL
i. DL+WL+TL
j. DL+EL+TL
k. DL+IL+WL+TL
l. DL+IL+EL+TL
(DL=deadload,IL=imposedload,WL=windload,EL=earthquakeload,TL=temperatureload).
Note1Whensnowloadispresentonroofs,replaceimposedloadbysnowloadforthepurposeofaboveloadcombinations.
Note2Therelevantdesigncodesshallbefollowedforpermissiblestresseswhenthestructureisdesignedbyworkingstressmethodandforpartialsafetyfactorswhenthestructureisdesignedbylimitstatedesignmethodforeachoftheaboveloadcombinations.
Note3Wheneverimposedload(IL)iscombinedwithearthquakeload(EL),theappropriatepartofimposedloadasspecifiedinIS:1893J984*shouldbeusedbothforevaluatingearthquakeeffectandforcombinedloadeffectsusedinsuchcombination.
Note4Forthepurposeofstabilityofthestructureasawholeagainstoverturning,therestoringmomentshallbenotlessthan12timesthemaximumoverturningmomentduetodeadloadplus14timesthemaximumoverturningmomentduetoimposedloads,Incaseswheredeadloadprovidestherestoringmoment,only09timesthedeadloadshallbeconsidered.Therestoringmomentsduetoimposedloadsshallbeignored.Incaseofhighwatertable,theeffectsofbuoyancyhavetobesuitablytakenintoconsideration.
Note5Incaseofhighwatertable,thefactorofsafetyof1.2againstupliftaloneshallbeprovided.
Note6Thestructureshallhaveafactoragainstslidingofnotlessthan14underthemostadversecombinationoftheappliedloads/forces.Inthiscase,only09timesthedeadloadshallbetakenintoaccount.
Note7Wherethebearingpressureonsoilduetowindaloneislessthan25percentofthatduetodeadloadandimposedload,itmaybeneglectedindesign.Wherethis
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exceeds25percentfoundationmaybesoproportionedthatthepressureduetocombinedeffectofdeadload,imposedloadandwindloaddoesnotexceedtheallowablebearingpressurebymorethan25percent.Whenearthquakeeffectisincluded,thepermissibleincreaseisallowablebearingpressureinthesoilshallbeinaccordancewithIS:18931984*.
Reducedimposedload(IL)specifiedinPart2ofthisstandardforthedesignofsupportingstructuresshouldnotbeappliedincombinationwithearthquakeforces.
Note8Otherloadsandaccidentalloadcombinationsnotincludedshouldbedealtwithappropriately.
Note9Craneloadcombinationsarecoveredunder/Part2ofthisstandard(see6.4ofPart2ofthisstandard).
*Criteriaforearthquakeresistantdesignofstructures(fourthrevision).
(Continuedfrompage2)
PanelonLoads(OtherthanWindLoads),BDC37:P3
Convener Representing
ShriT.N.SubbaRao GammonIndiaLimited,Bombay
DrS.V.Lonkar(Alternate)
Members
ShriS.R.Kulkarni M.N.Dastur&CoLtd,Calcutta
ShriM.L.Mehta Metallurgical&EngineeringConsultants(India)Ltd,Ranchi
ShriS.K.Datta(Alternate)
ShriT.V.S.R.AppaRao StructuralEngineeringResearchCentre,CSIRCampus,Madras
ShriNageshR.Iyer(Alternate)
ShriC.N.Srinivasan C.R.NarayanaRao,Madras
SuperintendingEngineer(D) CentralPublicWorksDepartment(CentralDesignsOrganization),NewDelhi
ExecutiveEngineer(D)VII(Alternate)
DrH.C.Visvesvaraya NationalCouncilforCementandBuildingMaterials,NewDelhi
BUREAUOFINDIANSTANDARDS
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