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Comprehensive Analysis of Modifications in the Draft Code IS1893 (WC) 2023 for RC Buildings

Dr. Dhara Shah1

1Sr. Assistant Professor, F aculty of Technology, CEPT University, Ahmedabad-09

Abstract - The latest draft of the building code IS 1893 (WC) Part1 & Part 2, issued by the Bureau of Indian Standards (BIS) in April 2023, introduces significant alterations and provisions necessitating careful scrutiny before enforcement. Key changes include the transition from Deterministic Seismic Hazard Assessment (DSHA) to Probabilistic Earthquake Hazard Assessment (PEHA) methodology for seismic zone factor determination, leading to substantial increase in peak ground accelerations and distinct seismic zone factors for strength design and serviceability checks within the same structure. This exodus hints a substantial shift towards performance-based seismic design practices. Moreover, adjustments to the horizontal response spectrum curve, expansion of soil site classification based on shear wave velocity, and modifications in load combinations, minimum design horizontal base shear force, lateral storey drift limits, and allowable structural systems in reinforced concrete (RC) buildings have been implemented. Furthermore, the draft code introduces novel criteria for assessing building irregularities, with a specific focus on torsion, and mandates consideration of soil flexibility in structural analysis. It also incorporates provisions for analyzing Architectural Elements and Utilities (AEU), addresses small residential structure design, and delineates torsional analysis criteria for rectangular regular buildings. While these revisions aim to enhance seismic design methodologies, challenges such as comprehending return periods and adapting to new methodologies may arise. Therefore, the provision of clear explanations within the code and educational resources is imperative to facilitate understanding and implementation. This research paper conducts a comprehensive analysis of the revisions introduced in the draft code, particularly focusing on their implications for RC buildings.

Key Words: Draft building code IS 1893 (WC) part 1 & part 2, peak ground accelerations, Probabilistic Earthquake Hazard Assessment, shear wave velocity

1. INTRODUCTION

ThelatestdraftofthebuildingcodeIS1893(WC)Part1&Part2releasedbyBISinApril2023[1][2]havebroughtsubstantial changesandprovisionsthatwarrantthoroughreview.Whilethefinalversionoftherevisionisanticipatedtocloselyresemble thisdraft,it'sessentialtoacknowledgethepossibilityofmodificationsinvaluesorspecificationsbeforeitsimplementation.It's worthnotingthattheimminentreleaseofIS1893Parts3to11,whichencompasstopicsrangingfromtankstotunnelsand more,isanticipatedinthenearfuture.

Part1:Generalprovisions

Part2:Buildings

Part3:Liquidretainingtanks

Part4:Bridgesandretainingwalls

Part5:Industrialstructures

Part6:Baseisolatedbuildings

Part7:Pipelines

Part8:Damsandembankments(tobeformulated)

Part9:Coastalstructures(tobeformulated)

Part10:Steeltowers(tobeformulated)

Part11:Tunnels(tobeformulated)

SomenoteworthychangesoutlinedinthedraftofthebuildingcodeIS1893(WC)Part1&Part2arepresentedhere.

1.1 Interpreting part 1 & part 2 together

TheexistingIS1893-2016Part1encompassesgeneralprovisionsandguidelinesforseismicdesignofbuildings,whileIS 1893(WC)Part1andPart2serveascomplementarysectionstobeinterpretedtogether.Part1typicallyaddressesgeneral provisions, while Part 2 specifically focuses on seismic design considerations for buildings. It could potentially introduce confusion or make the code less user-friendly if essential provisions for seismic design are spread across multiple parts. ConsolidatingallpertinentinformationintoPart1ofthecodewouldlikelystreamlinethedesignprocessandfacilitateeasier

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referenceforpractitioners.Thisapproachensuresthatcriticalseismicdesignconsiderationsarereadilyaccessiblewithina singledocument,enhancingclarityandusability.

1.2 Symbols & Notations

ThemajorityofsymbolsandnotationsinIS1893(WC)Part1andPart2,arenewlyintroducedandcausingconfusion comparedtothepreviousversionofthecode,highlightingasignificantusabilityissue.

1.3 Seismic zone factor

Thecornerstoneofthealterationsinthecodeisthemethodologyusedtodeterminezonefactors.Thenewseismicmapof IndiaisbasedonProbabilisticEarthquakeHazardAssessment(PEHA)[3]methodwithanadditionalzone–ZoneVI.Previous versions relied on the Deterministic Seismic Hazard Assessment (DSHA) approach. The design earthquake zone factor Z, indicativeofthemeanhorizontalpeakgroundacceleration,nowvariesbasedondifferentreturnperiods -TRP (years)for variousstructurecategorieswithineachzone.Peakgroundaccelerationshavesubstantiallyincreasedcomparedtoexisting values. Additionally, separate zone factors are now applicable for strength design and serviceability checks to the same building.Thisshiftrepresentsamomentousexodusfromearlierpractice,hintingasteptowardsperformancebasedseismic designofstructures. ThemethodforspecifyingthezonefactorsZinthedraftcodeinvolvesreferencingtwotables:Table1for obtainingthereturnperiod(TRP)applicabletoeachbuildingcategory(differentiatingbetweenDesignandServiceability),and Table2fordeterminingthecorrespondingzonefactorZbasedontheTRP andtheseismiczoneofthelocation.AppendixGof thedraftcodepart1givesabriefoftheprocess.

Inthecurrentcode,seismicintensityisdefinedusingtwodistinctcategories:MaximumConsideredEarthquake(MCE)and DesignBasisEarthquake(DBE)[4].ZonefactorZrepresentsMCEandtheDesignBasisEarthquakeistakenas50%ofMCEi.e. Z/2.Noteveryonemaybefamiliarwiththeconceptofreturnperiodsinseismicdesign.Returnperiodsrepresenttheaverage intervaloftimebetweenoccurrencesofaspecificseismiceventwithacertainmagnitudeatagivenlocation.Toaddressthis knowledgegap,it'simportantforseismicdesigncodestoprovideclearexplanationsandcontextregardingreturnperiods.This couldincludedefinitionswithinthecodeitself,aswellaseducationalmaterialsorreferencestoresourceswhereuserscan learnmoreaboutseismicterminologyandconcepts.Additionally,codecommitteecouldconsiderprovidingpracticalexamples orguidanceonhowreturnperiodsareusedinseismicdesigncalculations.Thiscanhelpusersunderstandthesignificanceof returnperiodsandhowtheyinfluencedesigndecisionswithoutrequiringspecializedexpertiseinseismology.

Nuclearpowerplant structures

TobespecifiedbyAtomicEnergy RegulatoryBoard(AERB),GoI

To be specified by Atomic Energy RegulatoryBoard(AERB),GoI

Table -1: Return Period TRP (years) for Strength Design and Serviceability [1]

Table -2: Earthquake Zone Factor Z for Different Return Periods TRP in Different Earthquake Zones [2]

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Table -3: Earthquake Zone Factor Z (MCE) [4]

Earthquakelevelsarecategorizedbasedontheirprobabilityofoccurrenceasfrequent,occasional,rare,veryrareandso on.Afrequentearthquakehas50%chanceofoccurrencein50yearswitha returnperiod-TRP of72years.Itisknownas serviceabilityearthquakeasperexistingcode. Alltypesofstructuresaredesignedtoremainfullyoperationalandfunctional undertheexpectedlevelsofshakingassociatedwiththeseearthquakes.Arareearthquakehas10%chanceofoccurrencein50 yearswithareturnperiod-TRP of475years.Itisknownasdesignearthquakeasperexistingcode.Criticalinfrastructureand importantstructuresaredesignedtoremainoperationalandfunctionalundertheexpectedlevelsofshakingassociatedwith theseearthquakes.Averyrareearthquakehas2%chanceofoccurrencein50yearswithareturnperiod-TRPof2475years.Itis knownasmaximumconsideredearthquakeasperexistingcode.Thislevelofseismiceventservesasabenchmarkforensuring thesafetyandresilienceofcriticalandlifelinefacilities.Thistypologyhintstheshifttowardsperformancebasedseismicdesign asperFig-1.

ThecomparisonofzonefactorsfordesignstrengthaspercategoryofstructuregivenindraftcodeisshowninTable4and comparedwiththezonefactorofthecurrentcode.

Table -4: Zone Factor comparison for design strength (current code and draft code)

be specified by AERB, Government of

Fig -1:PerformanceBasedSeismicDesign(PBSD)-SEAOCVision2000Committee(1995)[5]

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2. SEISMICITY AND IMPORTANCE

TheseismiczonemapofIndiahasbeenmodifiedinthedraftcodewithadditionalzone–zoneVIasshowninFig.2.Dueto changeinboundaries,manycitieshaveshiftedfrompreviouszonetohigherzone.Shimla,Chandigarh,RoorkeeandDehradun shiftedfromzoneIVtoVI.MaduraiandTrichyshiftedfromzoneIItoIII.Theentirenortheastbelt,northernpartandHimalayan regionalongwithwestGujaratisshiftedtonewzoneVI[2].

Seismic zone map India - draft code

Seismic zone map India - current code

Fig-2: SeismiczonemapIndia-draftcode&currentcode

2.1 Importance factor I

Inthedraftcode,theimportancefactorIvarydependingonthecategoryofstructuresandtheassociateddesignreturn period.Thecurrentcodeprovidesthreebasicvaluesforimportancefactor.Tablebelowshowsthecomparisonofimportance factorIaspercurrentcodeanddraftcode.

Table -5: Importance factor I

bespecifiedbyAtomic

RegulatoryBoard (AERB),GovernmentofIndia

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2.2 Response reduction factor R

Inthedraftcode,theresponsereductionfactoristermedaselasticforcereductionfactorR.Forbuildingsystems,itismore orlesssameascurrentcodeexceptatfewplaces.Table6belowhighlightsthedifferenceinvalueofRaspercurrentcodeand draftcode.FromthetableitisobservedthatthedraftcodehasprovideddifferentvalueofRforductilestructuralwallswithout boundaryelementsandwithboundaryelements.Additionally,fordualstructuralsystemtheincreaseinRvaluefrom5.0to5.5 and6.0couldpotentiallyleadtocostsavingsbyallowingformoreefficientdesignandconstructionofhigh-risebuildings.

Table -6: Response reduction factor R Structural system

BuildingwithOrdinaryBracedFrames(OBF)havingconcentricbraces

BuildingwithSpecialBracedFrames(SBF)havingeccentricbraces

Unreinforcedmasonry(designedanddetailedasperIS1905)andprovidedwith horizontalRCseismicbands

BuildingswithductileRCStructuralWallswithoutboundaryelements

withductileRCStructuralWallswithboundaryelements

Dual system - Buildings with ductile RC Structural Walls without boundary elementsandRCSMRF

Dualsystem-BuildingswithductileRCStructuralWallswithboundaryelements &RCSMRF

2.3 Response spectrum curve & design acceleration coefficient Sa/g:

Inthedraftcode,thehorizontalresponsespectrumcurvehasbeenextendedto10secondsunlikethecurrentcodeupto4 secondssoastoincorporatestructureswithhighertimeperiodsuchastallbuildings.Thenormalizedhorizontalpseudo spectralacceleration(PSA)ANH(T)correspondingtodampingof5percentofcritical,foreachsiteasperdraftcodeforusein Lineardynamicmethod–responsespectrummethodandforuseinlinearequivalentstaticmethodisshowninFig.3andFig. 4.Thecurrentcodecurveshavebeenextendedto10secondshereforbettercomparison.Forvaluesofdampingξ,otherthan5 percent(0%<ξ<30%),thenormalizedhorizontalPSAANH(T)shallbeobtainedaspertheequationsgiveninthedraftcode.

Fig-3: Horizontalspectrumcurvecomparisonforresponsespectrummethod (Solidlinesrepresentdraftcode,dottedlinesrepresentcurrentcode)

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Fig-4: Horizontalspectrumcurvecomparisonforequivalentstaticmethod (Solidlinesrepresentdraftcode,dottedlinesrepresentcurrentcode)

Thesoilsiteclassificationtoselectappropriateresponsespectrumcurvehasbeenmodifiedinthedraftcode.Thecurrent codeappearstousetheSPT(StandardPenetrationTest)“N”valueforsoilclassification[4]asshowninTable7whereasthe draftcodeproposestouseshearwavevelocityVS ofthesoilforclassificationasshowninTable8.Itisbasedontheweighted averageVS oftheunderlyingsoilstratainthetop30m.Thereisnodirectreferenceindraftcodewhichrelatesshearwave velocityandNvalueofasoil.InternationalBuildingCode[6]clearlyrelatessoilsiteclasswithaverageshearwavevelocityVS, NvalueandAverageundrainedshearstrengthofagivensoilasshowninTable9.Comparingthese,wecanconcludethatthe soiltypeA,BandCasperdraftcodecorrespondstotypeIsoilofthecurrentcode.TypeDsoilaspartlytypeIandpartlytypeII andtypeEsoilaspartlytypeIIandpartlytypeIII.NoresponsecurveisprovidedfortypeEsoilindraftcodewhichispartly undertypeIIIsoilaspercurrentcode.

Table -7: Soil type Classification (current code)

Soil Class

SPT value N

Type A – RockorHardsoils(TypeI) >30

Type B –Mediumorstiffsoils(TypeII) 10-30

Type C –Softsoils(TypeIII) <10

Type D –Unstable,collapsible,liquefiablesoils Requiressitespecificstudy

Table -8: Site Classes for estimating Normalized PSA (draft code) [2]

Site Class

Weighted Average Shear Wave Velocity VS - (m/s)

Lower Limit Upper Limit

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Table -9: Site Class Definitions, International Building Code IBC-2009 [6]

Site Class

A:HardRock

Average shear wave velocity (Vs)

Average standard penetration resistance (N1 or Nch)

Average undrained shear strength in the case of cohesive soils (su)

>1500m/s Notapplicable Notapplicable

B:Rock 760to1500m/s Notapplicable Notapplicable

C:Verydensesoilorsoftrock 370to760m/s >50 >100kPa

D:Stiffsoil

180to370m/s 15to50 50to100kPa

E:Softsoil <180m/s <15 <50kPa

Anyprofilewithmorethan3mofsoilhavingPlasticityIndexPI>20, Moisturecontentω≥40%,Averageundrainedshearstrengthsu<24kPa

F:Soilsrequiringsite-specific evaluation

Soilsvulnerabletopotentialfailureorcollapse(liquefiable,quick-orhighly sensitiveclays,collapsibleweaklycementedsoils)

Morethan3mofpeatand/orhighlyorganicclays

Morethan7.5mofveryhighplasticityclays(PI>75)

Morethan37mofsofttomediumclays

Theverticalresponsespectrumhasbeenmodifiedinthedraftcode.Thenewformulavarieswiththeperiod(T)ofthe structure'sresponse,asopposedtothecurrentcode,whichemploysaflatlinewithSa/gas2.5asshowninFig.5.Inthecurrent code,theflatlineeffectuallyrepresentsSa/gvalueof0.83,achievedthroughacalculationinvolvingthemultiplicationof2.5x (2/3)x(1/2),where(1/2)accountsfortheconversionfromMCEtoDBE.

Fig-5: Verticalspectrumcurvecomparison (Solidlinesrepresentdraftcode,dottedlinesrepresentcurrentcode)

3. DESIGN HORIZONTAL BASE SHEAR

TheseismichorizontalcoefficientAh fordesignasperthecurrentcodeistakenas

Ah = Z/2 * I/R * Sa/g (1) where,

Z=zonefactorforMCEasperTable3

I=Importancefactor

R=Responsereductionfactor

Sa/g=Designaccelerationcoefficientfordifferentsoiltypes

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TheelasticmaximumhorizontalPSAAHD(T)fordesignasperthedraftcodeistakenas

AHD(T) = Z * I/R * ANH(T) (2) where,

Z=zonefactorasperTable1andTable2

I=Importancefactor

R=Elasticforcereductionfactor

ANH(T) =Normalizedhorizontalpseudospectralacceleration(PSA)fordifferentsoiltype

3.1 Load combinations and partial load factors

Inthedraftcode[2],forlimitstateofstrength,thefollowingcombinationsareconsideredwhenearthquakeeffectsare combinedwithdeadandimposedloads.

 1.5DL+1.5LL

 1.2DL+1.2LL±EED

 1.5DL±EED

 0.9DL±EED

Whenperformingtheserviceabilitycheckofstructures,thefollowingcombinationsareconsideredwhenearthquakeeffects arecombinedwithDeadandImposedLoads.

 DL+LL

 DL+0.8LL±EES

 DL±EES

 0.9DL±EES

HereEEDisearthquakeloadfordesignandEESisearthquakeloadforserviceability.

The draft code proposes a partial load factor of 1.0 for earthquake loads in both design and serviceability combinations, contrastingwiththecurrentcode'suseofaloadfactorof1.5.ThismodificationiscreditedtothevigilantselectionofTRPaimed at accounting for qualms epitomized by partial safety factors. This can be proved by taking example of normal structure category and comparing Z values and partial load factors as shown in Table 10. Simultaneously, it's a concern for cities currentlydesignatedasZoneIV,facingaproposedshifttoZoneVIinthedraft,accompaniedbysubstantialincreasesinvalues for1.2(DL+LL+EQ)by247%andfor1.5(DL+EQ)by177%.

Table -10: Zone factor and partial load factor comparison (current code and draft code IS1893) Seismic Zone

Shimla, Chandigarh, Roorkee, Dehradun

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3.2 Minimum Design Horizontal Base Shear Force

Asperthedraftcode,theminimumdesignhorizontalearthquakebaseshearforceVBD,H forstrengthdesignshouldbe VBD,H, min = 0.625 * Z * I/R * W > 0.015W i.e. 1.5% where,

Z=zonefactorasperTable1andTable2

I=Importancefactor

R=Elasticforcereductionfactor

W=Seismicweightofthebuilding

TheequationclearlystatesthattheminimumvalueofANH(T)shouldbe0.625.Italsohighlightsthatinanycasethezonefactor Zshouldnotbelessthan0.12consideringnormalductilestructure.Theminimumdesignhorizontalearthquakebaseshear forceforstrengthaspercurrentcodeisshowninTable11.

Table -11: Minimum Design Earthquake Horizontal Lateral Force, current code [4]

4. Lateral Storey Drifts & structural systems in Buildings

Thedraftcodehasundergonechangesinthepermissibledriftlimitsaswell.ThelimitsaretobetakenfromZforserviceability andreducedforhigherzonesasshowninTable12,resultinginstrictercriteriaforhigherzones.Thecurrentcodeimposesa uniformrestrictiononstoreydrifts,limitingthemto0.004forbuildingsregardlessoftheseismiczones.

Table -12: Lateral Storey Drifts in Buildings as per draft code

Seismic Zone Lateral Storey Drifts

4.1 Admissible structural systems in RC Buildings

ThestructuralsystemspermittedasperdraftcodeforRCbuildingsareoutlinedinTable13,emphasizingthatrelying solely on moment frames may not yield optimal performance in higher seismic zones. Table 13 should be interpreted in conjunctionwiththeminimumStructuralPlanDensity(SPD)ofStructuralWallsinRCBuildingsasoutlinedinTable14,with zone-specificlimits.Notably,therearespecificprovisions,suchastherequirementforshearwallsinbuildingsonslopes(Fig.6 andTable15tobereferredtogether),aimedatmitigatingtorsionaleffectsinsuchstructures.Thenotationsgivenare:

OMRS=OrdinaryMomentResistingFrames

SMRF=SpecialMomentResistingFrames

SMRF+SSW=SpecialMomentResistingFrameswithSpecialStructuralWalls

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Table -13: Admissible structural systems in RC Buildings as per draft code

Seismic Zone

Building Category

Normal Important

II OMRF

SMRF

SMRF+SSW

DualSystem

III SMRF

SMRF+SSW

DualSystem

IV SMRF+SSW

DualSystem

SMRF

SMRF+SSW

DualSystem

SMRF

SMRF+SSW

DualSystem

Critical and Lifeline

SMRF+SSW DualSystem

SMRF+SSW DualSystem DualSystem

V DualSystem DualSystem DualSystem

VI DualSystem DualSystem DualSystem

Table -14: Minimum Structural Plan Density of Structural Walls alone in RC Buildings

Seismic Zone

Minimum Structural Plan Density of Structural Walls - SPD

Table -15: RC Wall Configurations in Step-Back Buildings on Hill Slopes

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4.2 Small residential Buildings

Thedraftcodeadoptsalenientapproachtowardsthedesignofsmallresidentialframedstructuresuptotwostoreys (includingbasement),wheretheEquivalentStaticMethodofanalysissuffices.However,inzonesIIandIII,itmandatesatleast SpecialMomentResistingFrames(SMRF)withinfillwallscoveringaminimumof90%ofthebays.In zonesIVandV,the requirementisforatleastSMRF(withinfills)alongwithSpecialShearWalls(SSW),ensuringaminimumof1.5%Structural PlanDensity(SPD)ineachprincipalplandirection.

4.3 3D Modeling and soil stiffness

Thedraftcodenowmandatestheconsiderationofsoilflexibilityforallcases,demandingthatbuildinganalysismodels havetheirsupportsassignedwithcalculatedspringsratherthanbeingfixedorpinned. ForLinearEquivalentStaticAnalysis withoutexplicitlyconsideringinertialeffects,it'sessentialtoaccountforflexiblesoiltranslationaland/orrotationalsprings intotheanalysis.It’sessentialtoincorporateallaspectsofsoil-structureinteractionwhenperformingDynamicAnalysisforthe structureunderdesignorevaluation.However,thisrequirementexcludesbuildingsinsiteclassesAandB,aswellasthoseup tofivestoreysinheightrestingonindividualfootings.Inthedraftcode,theflexibilityofsoiliscapturedthroughitsmodulusof subgradereactionfordifferentfoundations.

4.4 Soil damping

Oneofthenumerousenhancementstothecodeistheintroductionofsoildampingforthepurposeofdesign.Thedamping ratioofsoilistobetakenas2.5percent.But,forassessmentofstructuresunderearthquakeloading,itisrequiredtousestraindependenthystereticdampinginsteadofviscousdamping,whenmodelingsoil.

5. TORSION IN BUILDINGS

Thedraftcodehasintroducedasignificantcriterionregardingbuildingirregularities,particularlycrucialfortallstructures, focusingontorsion.Theexistingcriterioninthecurrentcodeidentifiesabuildingastorsionallyirregularwhentheratioof maximumflooredgedisplacement∆maxtoitsminimum∆minexceeds1.5timesasshowninFig.7.Inadditiontoit,thedraftcode

Fig- 6: ShearWallConfigurationsforBuildingsonSlopeasperdraftcode

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specifiesTorsionalFlexibilityFactor,ψofthebuilding,derivedbyevaluatingtheinfluencesofthreeaspectscontributingtothe building's torsional tendencies. If ψ < 0.4, the building is said to be torsionally stiff else is termed as torsionally flexible. TorsionalFlexibilityFactoriscalculatedas

where,

B=OuterDimensionofthebuildingalongthedirectiontotheconsidereddirectionofshaking

eK =StiffnesseccentricityofthebuildingwithrespecttoCR

eK

= Normalized stiffness eccentricity of the building

r = Translational radius of gyration of the mass of the building at the floor level

rKθ = Torsional Radius of gyration of the mass of the building at the floor level

τ =RatioofNaturalPeriodsofFundamentalTorsionalandFundamentalTranslational Modesofoscillationofthebuilding,i.e.T

or Tθ / TY for considered direction of shaking of X and Y

Fig- 7: TorsionalIrregularityinBuildings

Inthecaseofrectangularregularplanbuildings,thedecisiontoconducteitheratorsionalanalysisorrevisethestructural configurationisdeterminedbyconsideringthetorsionaleccentricityandtheratiooftheτ'sasspecifiedinTable16.However, forbuildingswithnon-rectangularirregularplangeometry,itmustbeensuredthattheTorsionalFlexibilityFactor-ψisless than0.4.Otherwise,thestructuralconfigurationneedstoberevised.

Table -16: Design Limit foreK and τ for Rectangular Regular Buildings

6. ARCHITECTURAL ELEMENTS &UTILITIES (AEU)

AsignificantenhancementtothecodeistheinclusionofanalysisforArchitecturalElementsandUtilities(AEU),previously mainlyfoundinNDMAguidelinesbutnowintegratedintothedraftcode.AEUencompassesvariousappendages,rangingfrom partitionwallsandstoragecabinetstoelectricalandmechanicalequipment.Theyarecategorizedasacceleration-sensitive AEUsanddisplacement-sensitiveAEUs,withthelatterfurthersubdividedbasedonwhethertheyarefixedatdifferentbuilding levels or at the same level. The code elaborates on methods of analysis for each category, providing dedicated tables for Importance,AccelerationAmplification,andResponseReductionfactorsforreference.ThedesignlateralforceFpforthedesign ofanchoragesconnectingAcceleration-SensitiveAEUstotheStructuralElements(SEs)ofthebuildingshallbetakenas:

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Where,

Z =Earthquakezonefactor asperTable2ofdraftcodeforthe earthquakezoneofthesiteofthestructureonwhichtheAEU ismounted,givenbytheEarthquakeZoneMapofIndia(Fig.1)

��=HeightofthepointofattachmentofAEUabovetopofthefoundationofthestructure

H=Overallheightofthestructureabovetopofthefoundation

��AEU = ImportancefactoroftheAEU(Table17)

��AEU =AccelerationAmplificationFactoroftheAEU(Tables11and12ofdraftcode)

��AEU =ElasticForceReductionFactoroftheAEU(Tables11and12ofdraftcode)

��AEU =Weightofthe AEU

Theprovisionofthisclauseisequallyapplicableforthedesignofinfillwallsandpartitionwallsthatareplacedwitha gap betweenthestructuralelements,sothatthesewallsdonotfoulwiththelateraldisplacementofthestructuralelements,the provisionsoftheseclausesshallbeapplicable.

Table-17: Importance Factor ��EU of AEUs

racksinstructuresopentothepublic

7. SUMMARY & CONCLUSIONS

 ThemomentouschangesintheDraftcodesofIS1893,incomparisontothecurrent2016edition,arehighlighted. Notably,inthedraftcode,zonefactorsaredeterminedbasedonProbabilisticSeismicHazardAssessment(PSHA), divergingfromtheDeterministicSeismicHazardAssessment(DSHA)approachutilizedthecurrentcode.Wang[7]sees PSHAasapurelynumericalconceptwithoutphysicalormathematicalbasiswhichcouldleadtoengineeringdesigns thatareeitherunsafeoroverlycautious,withseriousconsequencesforsociety.AlsoKrinitzsky[8]arguesthatPSHAis aflawedprocedure.

 Thecodecomplicatesthewell-understoodconceptsof MaximumConsideredEarthquake(MCE)andDesignBasis Earthquake(DBE)byexcludingthefactor'2'fromtheexpressionforAh,whichisrecognizedbystructuralengineers. Consequently,structuralengineersmaylackclarityonwhethertheyaredesigningfortheactualearthquakeforcesor forreducedvalues.

 Thecodeundervaluestheimportancefactor'I'bytypicallysettingitsvalueto1.0,renderingitinsignificant.

 Theearthquakeloadfactor,previouslyspeciouslysetat1.5inearlierversions,isnowcorrectlyacknowledgedas1.0.

 WhiletheexistingcodeusestheSPTvalueofsoilforclassification,thedraftcodeemploystheshearvelocityofsoil,Vs, forthispurpose.

 Theallowabledriftlimitsaresternerforthehigherzones.

 ThedraftcoderecommendsspecificstructuralsystemsforRCbuildingsacrossdifferentzones,alongsideminimum requirements for Structural Plan Density (SPD) of structural walls.Implementing these guidelines, particularly in severezones,mayposechallengesandcouldpotentiallyconstrainthecreativityofarchitectsandengineers.

 Animportantaspectinvolvesincorporatingshearwallsinbuildingslocatedonslopestomitigatetorsionaltendencies. Toaddressthis,anewprovisionhasbeenintroducedforcalculatingtheTorsionalFlexibilityFactor,aimingtoreduce torsionalirregularitiesinthebuildingdesign.

 FEMAP-2012[9]conductedcollapseanalysesondifferenttypesofbuildings,bothwithandwithoutirregularities. Their findings exhibited that the Equivalent Lateral Force (ELF) method tends to yield more conservative results comparedtoResponseSpectrumAnalysis(RSA),aligningmorecloselywiththeforceoutcomesderivedfromNonlinear Time-History Analysis. Consequently, the ELF method is recommended in the latest ASCE 7-22 [10] with fewer limitations.However,it'snotedthattheproposedcodalprovisionsoverallleantowardsbeingoverlycautious.

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REFERENCES

[1] CED 39(22343) WC, "Draft Indian Standard Criteria for Earthquake Resistant Design of Structures Part 1 General Provisions[SeventhRevisionofIS1893(Part1)](ICSNo.91.120.25),"BureauofIndianStandards,NewDelhi,2023.

[2] CED 39 (22345) WC, "Draft Indian Standard Criteria for Earthquake Resistant Design of Structures Part 2 Buildings [SeventhrevisionofIS1893(Part1)](ICSNo.91.120.25),"BureauofIndianStandards,NewDelhi,2023.

[3] NDMA,"ProbabilisticSeismicHazardMapofIndia-Finalreport,"NationalDisasterManagementAuthority,India,New Delhi,2022.

[4] IS1893part-1,"CriteriaforEarthquakeResistantDesignofStructures:Part1-GeneralprovisionsandBuildings,"Bureauof Indianstandards,NewDelhi,2016.

[5] SEAOC, "Vision2000, Performance Based Seismic Engineering of Buildings, Vols. I and II: Conceptual Framework," StructuralEngineersAssociationofCalifornia,USA,2000.

[6] IBC,"InternationalBuildingCode,"WashingtonStateBuildingCodeCouncil,USA,2009.

[7] WangZ.,"SeismicHazardAssessment:IssuesandAlternatives,"PureandAppliedGeophysics,p.11–25,2010.

[8] KrinitzskyE.L.,"Deterministicversusprobabilisticseismichazardanalysisforcriticalstructures,"EngineeringGeology, vol.Volume40,no.1–2,pp.1-7,1995.

[9] FEMA P -2012, "Assessing Seismic Performance of Buildings with Configuration Irregularities-Calibrating Current StandardsandPractices,"AppliedTechnologyCouncilfortheFederalEmergencyManagementAgency,Washington,D.C, US,2018.

[10] ASCE/SEI-7,"MinimumDesignLoadsandAssociatedCriteriaforBuildingsandOtherStructures,"AmericanSocietyof CivilEngineers,Reston,Virginia,USA,2022.

[11] SubramanianN.,LeslieR.,“ImpactofDraftIS1893-2023CodeProvisionsonBuildingDesign”,CE&CR,2023.

BIOGRAPHY

Dr.DharaShahisSr.AssistantProfessor,atFacultyofTechnology,CEPTUniversitysince2006.Hermajor areaofresearchincludesperformancebasedseismicdesignofstructures,fragilityanalysisofstructures, Vibrationimpactassessmentofheritagestructure,Marinestructures,Steel&RCCstructures.