commentary to assessment and improvement of unreinforced masonry buildings for earthquake resistance

7/26/2019 Commentary to Assessment and Improvement of Unreinforced Masonry Buildings for Earthquake Resistance

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FacultyofEngineering,TheUniversityofAuckland

Commentaryto

AssessmentandImprovementof

Unreinforced

MasonryBuildingsforEarthquake

ResistanceSupplementtoAssessmentandImprovementoftheStructuralPerformanceof

BuildingsinEarthquakes

Draft

12/2011


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Contents

SectionC1 HistoryandPrevalenceofUnreinforcedMasonryBuildingsinNewZealand..........11

C1.1Introduction.......................................................................................................................11

C1.3URMPerformanceinPastEarthquakes............................................................................13

C1.4NewZealandURMBuildingStock.....................................................................................18

C1.5NewZealandBuildingCodesPertainingtoURMConstruction......................................113

C1.6Acknowledgements.........................................................................................................118

C1.7References.......................................................................................................................118

SectionC2 MaterialPropertiesofMasonryWalls......................................................................21

C2.1Notation............................................................................................................................21

C2.3InsituandExtractedSampleTesting................................................................................21

C2.4BrickandMortarFieldAssessmentProcedure.................................................................25

C2.5AdditionalInformation......................................................................................................26

C2.7MasonryStressBlockParameters...................................................................................222

C2.8WorkedExamples............................................................................................................223

C2.9References.......................................................................................................................227

SectionC3 MaterialPropertiesofFlexibleTimberFloorDiaphragms........................................31

C3.3Timberproperties..............................................................................................................31

C3.4Classification......................................................................................................................33

C3.5ConfigurationandConditionAssessment.........................................................................33

C3.6CharacteristicValues.........................................................................................................35

C3.7DiaphragmStiffness........................................................................................................314

C3.8WorkedExample1..........................................................................................................315

C3.9WorkedExample2..........................................................................................................317

C3.10WorkedExample3........................................................................................................319

C3.11References.....................................................................................................................321

SectionC4 DesignActionsonInplaneLoadedUnreinforcedMasonryWalls............................41

C4.1Notation............................................................................................................................41

C4.2Scope.................................................................................................................................41

C4.3AnalysisProcedures...........................................................................................................41

C4.4DesignExample...............................................................................................................416


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C4.5References......................................................................................................................424

SectionC5 DeterminationofDiaphragmDesignActions...........................................................51

C5.2Scope.................................................................................................................................51

C5.3LoadDistribution..............................................................................................................51

C5.4DesignActions...................................................................................................................51

C5.5WorkedExample...............................................................................................................51

C5.6References........................................................................................................................53

SectionC6 DesignActionsonURMWallsandParapetsloadedoutofplane...........................61

C6.1Notations..........................................................................................................................61

C6.2Scope.................................................................................................................................61

C6.3DesignLateralForceonWallsloadedoutofplane..........................................................63

C6.4DesignExample.................................................................................................................63

C6.5References........................................................................................................................67

SectionC7 DesignActionsonWallDiaphragmAnchorages.......................................................71

C7.1Notation............................................................................................................................71

C7.2Scope.................................................................................................................................71

C7.3DesignShearforInplaneLoadedConnections................................................................71

C7.4DesignTensionforOutofplaneLoadedConnections.....................................................71

C7.5DesignExample.................................................................................................................72

C7.6References........................................................................................................................74

SectionC8 Responseofwallsloadedinplane...........................................................................81

C8.1Notation............................................................................................................................81

C8.2Scope.................................................................................................................................81

C8.3Propertiesofwallsloadedinplane..................................................................................83

C8.4NominalShearCapacityofwallsloadedinplane............................................................84

C8.5DeformationLimits...........................................................................................................89

C8.6WorkedExamples...........................................................................................................810

References..............................................................................................................................817

SectionC9 StrengthandDeformationAssessmentofFlexibleTimberFloorDiaphragms........91

C9.3LateralDeformation..........................................................................................................91

C9.4Strength............................................................................................................................91


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C9.5WorkedExample1............................................................................................................92

C9.6WorkedExample2............................................................................................................93

C9.7WorkedExample3............................................................................................................94

C9.8References.........................................................................................................................95

SectionC10 StrengthandDeformationAssessmentofTimberRoofDiaphragms...................101

C10.2Scope.............................................................................................................................101

C10.3MaterialProperties.......................................................................................................102

C10.4LateralDeformation......................................................................................................102

C10.5Strength.........................................................................................................................102

C10.6References.....................................................................................................................102

SectionC11 OutofplaneWallandParapetResponse.............................................................111

C11.2Scope.............................................................................................................................111

C11.3WallThickness,Height,andSlendernessRatio.............................................................112

C11.4Loadbearingwalls.........................................................................................................113

C11.5Assessment....................................................................................................................113

C11.6Workedexample...........................................................................................................117

C11.7References...................................................................................................................1113

SectionC12 WalldiaphragmAnchorages.................................................................................121

C12.1Notation........................................................................................................................121

C12.2Scope.............................................................................................................................121

C12.3DiaphragmJoistSeating................................................................................................123

C12.4MasonryAnchorageFailures.........................................................................................123

C12.5SteelAnchorageFailures...............................................................................................124

C12.6TimberAnchorageFailures...........................................................................................125

C12.7Examples........................................................................................................................127

C12.8References.....................................................................................................................129

Section C13 Heritage Characteristics of URM Buildings and the Impacts of Seismic

Improvements.............................................................................................................................131

C13.1Introduction...................................................................................................................131

C13.2HeritageandConservation............................................................................................132

C13.3ArchitecturalCharacter.................................................................................................137

C13.4InitialConsiderationsforSeismicImprovement.........................................................1315


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C13.5StabilisationforSeismicImprovement.......................................................................1317

C13.6EnhancingExistingWalls.............................................................................................1321

C13.7NewBuildingStrengtheningSystems.........................................................................1325

C13.8ReductionofForces....................................................................................................1331

C13.9ApproachestoSeismicImprovement.........................................................................1332

C13.10Conclusions...............................................................................................................1335

C13.11References................................................................................................................1336

Section C14 Methods for Stiffening and Strengthening of Flexible Timber Floor and Roof

Diaphragms.................................................................................................................................141

C14.2Scope.............................................................................................................................141

C14.3RetrofitSelection..........................................................................................................141

C14.4RevisedDiaphragmAssessment...................................................................................145

C14.5DiaphragmChordDesign..............................................................................................145

C14.6SubdiaphragmDesign...................................................................................................148

C14.7DiaphragmPenetrations...............................................................................................149

C14.8WorkedExample.........................................................................................................1410

C14.9References..................................................................................................................1410

SectionC15 MethodsforImprovingWallDiaphragmConnections.........................................151

SectionC16 UnbondedPosttensioning...................................................................................161

C16.1Notation........................................................................................................................161

C16.2Scope.............................................................................................................................162

C16.3PosttensioningTendonTypes,StressesandSpacing..................................................165

C16.4InplaneWallBehaviour................................................................................................166

C16.5OutofplaneWallBehaviour......................................................................................1610

C16.6DesignExample...........................................................................................................1615

C16.7References..................................................................................................................1619

SectionC17 SurfaceBondedFibreReinforcedPolymerSystems.............................................171

C17.2Notation........................................................................................................................171

C17.2Scope.............................................................................................................................172

C17.3GeneralDesignInformation..........................................................................................172

C17.4ShearStrengthProvidedbyFibreReinforcedPolymer................................................172


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Relatively little data is available for shear strengthenhancement usingvertical FRP systems,

andhenceaconstanteffectivestrainvalueisproposed......................................................1711

C17.5DesignExamples..........................................................................................................1711

C17.6References...................................................................................................................1716

SectionC18 NearSurfaceMounted(NSM)FibreReinforcedPolymerSystems.......................181

C18.1Notation........................................................................................................................181

C18.2Scope.............................................................................................................................182

C18.3RetrofitParameters.......................................................................................................183

C18.4InplaneDesign..............................................................................................................183

C18.5OutofplaneDesign......................................................................................................183

C18.6OtherConsiderations....................................................................................................187

C18.7Designexamples............................................................................................................189

C18.8References...................................................................................................................1813

SectionC19 FibreReinforcedShotcrete(FRS)..........................................................................191

C19.1Notation........................................................................................................................191

C19.2Scope.............................................................................................................................192

C19.3InplaneGeneralDesignInformation............................................................................193

C19.4OutofplaneGeneralDesignInformation....................................................................196

C19.5References...................................................................................................................1913

SectionC20 NearSurfaceMountedSteelReinforcement........................................................201

SectionC21 TextileReinforcedMortars....................................................................................211

SectionC22 RestrainingParapetsandChimneys......................................................................221

SectionC23 Pounding................................................................................................................231


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ListofFigures

FigureC11:Raupowhare(house)atWairauPa,ca.1880(AlexanderTurnbullLibrary)............11

FigureC12:RaupoandtimberwharesofaMaorivillageatMaketu,Kawhia,1895(Alexander

TurnbullLibrary)............................................................................................................................11

FigureC13: NewZealandtotalpopulationdata,18582007......................................................12

FigureC14:ShopsonQueenStreet,Auckland,1859(AlexanderTurnbullLibrary)....................13

FigureC15:QueenStreetandQueenStreetWharf,Auckland,in1882(AlexanderTurnbull

Library)..........................................................................................................................................13

FigureC16:GroupphotographoftheconstructionworkersthatbuilttheStratfordPublic

Hospitalduring19061907(AlexanderTurnbullLibrary).............................................................14

FigureC17:Brickbuildingunderconstruction,ca1920(AlexanderTurnbullLibrary)................14

FigureC18:The1833StoneStoreatKerikeriwasbuiltbytheChurchMissionarySociety.(AP

GodberCollection,AlexanderTurnbullLibrary)...........................................................................14

FigureC19:TwoChineseminersinfrontofastonecottageincentralOtago,ca1860(Alexander


FigureC110:Collapseofanewmasonryauctionmarketbuilding,QueenStreet,1865

(AlexanderTurnbullLibrary).........................................................................................................15

FigureC111:LookingalongarowofcommercialbuildingsonQueenStreet,Auckland,ca1910


FigureC112:VictorianChristchurchin1885(Coxhead1885).....................................................15

FigureC113:Christchurchsfirstskyscraper,photocirca1910(BrittendenCollection1910)..15

FigureC114:Generalstoredamagedbythe1929Murchisonearthquake(AlexanderTurnbull

Library)..........................................................................................................................................16

FigureC115:Damagedbusinesspremisesaftertheearthquakeof17June1929(Alexander


FigureC116:HastingsStreet,Napier,circa1914(AlexanderTurnbullLibrary)..........................16

FigureC117:ViewdownHastingsStreet,Napierafterthe1931earthquake(AlexanderTurnbull

Library)..........................................................................................................................................16

FigureC118:LookingoverNapieratthebuildingsruinedbythe1931earthquakeandthefires


FigureC119:RuinsoftheNapierAnglicanCathedralafterthe1931Napierearthquake


FigureC120:Toppledparapetinthe2007Gisborneearthquake...............................................18

FigureC121Outofplanefailureofagablewallinthe2007Gisborneearthquake...................18


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FigureC122:OutofplanewallfailureatthecornerofWorcesterandManchesterstreetsinthe

2010Darfieldearthquake..............................................................................................................18

FigureC123:Outofplanewallfailureat118ManchesterStreetinthe2010Darfield

earthquake....................................................................................................................................18

FigureC124:PhotographicexamplesofNewZealandURMtypologies......................................19

FigureC125:Estimated%NBSofURMbuildingsinProvincesthroughoutNewZealand.........112

FigureC21:Stepstodeterminebrickproperties.........................................................................22

FigureC22:Determinationofmortarcompressionstrength......................................................23

FigureC23:Preparationforprismcompressiontest...................................................................23

FigureC24:Masonryflexuralbondtest.......................................................................................24

FigureC25:Insituandlaboratorybedjointsheartest...............................................................24

FigureC26:Differencebetweenexposedandunexposedbricksurface.....................................26

FigureC27:Colourspectrumintensityvs.compressivestrengthplot........................................28

FigureC28:Brickcompressivestrengthvs.visiblecolourplot....................................................28

FigureC29:Plotofbrickcompressivestrengthvs.scratchindex..............................................210

FigureC210:PlotofMortarcompressivestrengthvs.scratchindex........................................211

FigureC211PlotofbrickModulusofRupturevs.brickcompressivestrength.........................212

FigureC212:Plotofmortarcompressivestrengthvs.h/tratio................................................213

FigureC213:3Dplotrelatingthebrick,mortarandmasonrycompressivestrengths.............215

FigureC214:PlotofmasonryModulusofElasticityvs.compressivestrengthplot..................215

FigureC215:Unreinforcedmasonrymodulefordensityapproximation..................................216

FigureC216:Plotofmasonryflexuralbondstrengthvs.masonrycompressivestrength........217

FigureC217:Differenttypesofbondfailure.............................................................................218

FigureC218:Plotofmasonryflexuralbondstrengthvs.mortarcompressivestrength...........218

FigureC219:Plotofshearstressvs.axialcompressionforlaboratorymanufacturedsamples220

FigureC220:Plotofshearstressvs.axialcompressionforfieldsamples.................................220

FigureC221:Plotofcohesionvs.masonrycompressivestrength.............................................221

FigureC222:Plotofcohesionvs.mortarcompressivestrength...............................................221

FigureC223:CampbellFreeKindergarten.................................................................................223

FigureC224:TwostoreyIrishPub.............................................................................................225

FigureC225:Twostoreycommercialbuilding...........................................................................226

FigureC31:Testpieceforembeddedstrengthtests...................................................................32


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FigureC32:Testsetupforembeddedstrengthtests..................................................................32

FigureC33:Pureblocktestsetuptodeterminecompressionstrengthofwood.......................33

FigureC34:Diaphragmconfigurationdetails..............................................................................34

FigureC35:Fullscalediaphragmtestingresults.........................................................................39

FigureC36:Idealisedbilinearresponsecurve...........................................................................310

FigureC37:Bilinearcurvesfromfullscalediaphragmtesting..................................................313

FigureC41:Modaltestingandsystemidentificationprocedure................................................47

FigureC42:PlotsofForcedisplacementresponseofURMassemblages.................................411

FigureC43:SeismichazardzonationfortheNorthIslandofNewZealandforgroundmotion

recordselection..........................................................................................................................414

FigureC44:Layoutofexamplebuilding....................................................................................417

FigureC61:FlowchartforOutofplaneSeismicDesignofURMbuildingswithFlexible

Diaphragms...................................................................................................................................62

FigureC62:Definitionofheights.................................................................................................63

FigureC63:Buildingcrosssection...............................................................................................64

FigureC81:Effectivepiermodel(Yietal.2008).........................................................................82

FigureC82:Shearstressdistributioninarectangularwall.........................................................83

FigureC83:Tributaryareasfordeterminingnormalforceoneachwall(Russell2010).............84

FigureC84:DiagonalTensionfailuremode.................................................................................85

FigureC85:Rocking/toecrushingfailuremode..........................................................................88

FigureC86:Bedjointslidingfailuremode..................................................................................89

FigureC87: Equivalentbilinearapproximation(MagenesandCalvi1997)..............................810

FigureC88:Planlayoutofbuilding............................................................................................810

FigureC101:Examplesofroofconfigurations...........................................................................101

FigureC111:ProcedureforseismicassessmentofoutofplaneloadedURMwalls................115

FigureC112:ZonationmapfortheNorthIsland.......................................................................116

FigureC113:ZonationmapfortheSouthIsland.......................................................................116

FigureC114:SummaryofNorthIslandparametricstudyresults(singlestorey2leafwall

Shallowsoil)................................................................................................................................117

FigureC121:Photographsofdamageinthe2010Darfield(Canterbury)earthquakedueto

deficientorabsentdiagramanchorages....................................................................................122

FigureC122: Examplesofwalldiaphragmanchoragesthatwerepartiallyorfullysuccessfulduringthe2010Darfieldearthquake.........................................................................................124


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FigureC123:Examplesoffailedanchorageswheresteelshowsnoindicationoffailure.........125

FigureC124:JoistorientedparalleltoURMwall.......................................................................126

FigureC125:JoistorientedperpendiculartoURMwall............................................................126

FigureC126:Observedrowfailuremodesfortimberconnectionsloadedparalleltograin....127

FigureC127:Assumedfailureplainforpunchingshearfailure.................................................128

FigureC131:TheBirdcagehotelpriortoseismicimprovementandbeingmoved...................132

FigureC132:NapierSchoolofMusicbeforeandafterretrofit.(reproducedfromRobinsonand

Bowman2000)............................................................................................................................137

FigureC133:BeforeandaftercrosssectionsthroughCranmerSquareNormalSchool,

Christchurch(reproducedfromWilby,1983).Showingchangedinteriorlayoutsandsurfacesand

removedalargeamountofthehistoricmaterial.......................................................................137

FigureC134:PrimaryformofaURMbuildinginAuckland.Atthisstagethebasicshapeandthe

broadgesturesthatmakeupthebuildingarenoted.Inthiscasethebuildinghasareasonably

simpleformanddisplaysatypical3partverticalhierarchy.......................................................139

FigureC135:Astudyofthebuildingsopeningsintwodimensions.Thishasbeendonefirstlyas

thephysicalopeningsintheURM,andsecondlyastheformssurroundingtheopenings.

Interferingwiththesepatternswillchangethewaythatthebuildingreads;somethingassimple

aschangingthecolourofthewindowframeswillbringtheseforwardandmaketheopenings

smallerandlessdistinct............................................................................................................1310

FigureC136:Shed13ontheWellingtonwaterfrontfeaturesadistinctiveroofthatisintegralwithitscharacter.......................................................................................................................1311

FigureC137:Aparapetthatisintegralwiththedesignoftherestofthefacadeandwhich

contributeshistoricinformation...............................................................................................1311

FigureC138:TheAucklandFerryBuildingisintegralwithitswaterfrontsettingandalteringthis

relationshipwouldremovehistoricmeaning...........................................................................1311

FigureC139:Detailsofopenings.Thingstotakenoteofherearethebondpatternand

techniqueusedforlayingbricks,colouring,strikingofmortar,changesinsurface,recessesand

depressions,andproportionsofwindowsandothercomponents..........................................1312

FigureC1310:ArcadesinAucklandwithcomplexspatialrelationshipswhereblockinglinesof

sightbetweenspacesorimpedingestablishedpedestrianrouteswillhavesignificantnegative

effects........................................................................................................................................1314

FigureC1311:Severelydegradedbrickandmortarduetomoisture......................................1318

FigureC1312:ParapetsstrengthenedusingnearsurfacemountedFRPstrips......................1319

FigureC1313:Anextremecaseinthe2010Darfieldearthquakewhereinadequateconnections

haveresultedinwallcollapse...................................................................................................1319

FigureC1314:Anassortmentofdiaphragmfixings.................................................................1320


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FigureC1315:Spiralthreadedrodsbeinginstalledtosecureanouterlayerofbricks...........1321

FigureC1316:Strutsfromthefloorabovetoimproveoutofplaneperformance................1323

FigureC1317:PosttensioningbarsusedintheBirdcagehotelwithconcreteloadspreaderscut

intothebrick.............................................................................................................................1324

FigureC1318:Simpleandvisuallyinterestinginplanestrengthening...................................1325

FigureC1319:PierdamagebetweenopeningsintheDarfieldEarthquake............................1326

FigureC1320:AconcretemomentframeinsidethefaadeofalargeURMbuildingin

Wellington(DunningThorntonConsultants)............................................................................1327

FigureC1321:Eccentricbracinginawalkway(DunningThorntonConsultants)....................1327

FigureC1322:Aneccentricallybracedcore(DunningThorntonConsultants).......................1327

FigureC1323:Shotcretewallsontherearofthebirdcagehotel............................................1329

FigureC1324:FRPappliedtoawall(DunningThorntonConsultants)...................................1329

FigureC1325:Itispossibletomakediaphragmimprovementsvisiblyinteresting,aswiththis

recentlyinstalledfloor..............................................................................................................1330

FigureC1326:Aroofbracingsystemwhichclasheswiththeexistingstructure,resultingina

confusedceilingspace..............................................................................................................1333

FigureC1327:Theornatefaadeofthisbuildingmadeexteriorstrengtheningdifficult.......1334

FigureC1328:Thesolutionwastoinnovativelystrengthentheinterior,whichallowedretention

ofitsmostimportantvisualelements......................................................................................1334

FigureC1329:OpeningsinthisChristchurchcafallowedplacementofframeswhich

complimentsthespace.............................................................................................................1334

FigureC1330:Steelstructureinstalledinanintrusivewaywhichisvisuallydistracting........1334

FigureC1331:Noattempthasbeenmadetoconcealthisnewshearwall,rathertheaestheticis

celebratedbytherestofthearchitecture................................................................................1335

FigureC1332:Excessivefloorandwalltiessomehowworkwiththisfaade.........................1335

FigureC141:Diaphragmretrofitexamples...............................................................................144

FigureC142:Photographsoftestedretrofitteddiaphragms....................................................146

FigureC143:Fullscaleretrofitteddiaphragmtestresults........................................................147

FigureC144:Diaphragmchordschematic.................................................................................147

FigureC145:Subdiaphragmexample(fromOliver2010).........................................................149

FigureC146:TypicalOutofPlaneWallSupportDetailatDiaphragmOpening(fromOliver2010)

..................................................................................................................................................1410

FigureC161:PosttensioningRetrofitTechnique......................................................................163

FigureC162:DefinitionofLimitStates......................................................................................163


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FigureC163:FlowchartforPosttensioningSeismicRetrofitDesign.........................................164

FigureC164:TypicalStressStrainPlots.....................................................................................165

FigureC165:PosttensionedInplanePierDefinitionandStressProfileatInitialState...........166

FigureC166:PosttensionedInplanePierEquilibriumatNominalStrengthLimitState.........167

FigureC167:PosttensionedInplanePierEquilibriumatFirstCrackingLimitState................168

FigureC168:PosttensionedInplanePierEquilibriumatHingeFormationLimitState...........169

FigureC169:TestFrameDimensions.......................................................................................1610

FigureC1610:CalculatedVsExperimentalValues...................................................................1610

FigureC1611:PosttensionedOutofplaneWallDefinitionandStressProfileatInitialState...16

11

FigureC1612:PosttensionedOutofplaneWallatNominalStrengthLimitState................1611

FigureC1613:CalculatedVsExperimentalValues...................................................................1614

FigureC1614:URMWallDetails..............................................................................................1616

FigureC171:ExamplesofFRPsystems......................................................................................172

FigureC172:ExamplesofnonverticalFRPretrofitsystems.....................................................174

FigureC173:ExamplesofverticalFRPretrofitsystems.............................................................174

FigureC174:FRPcontinuousfabricsystemextendedldbeyondthetopofthedoors.Thevertical

FRPsystemwasdesignedforthepierbetweenthetwodoors..................................................176

FigureC175:FRPdesignflowchart.............................................................................................177

FigureC176:TrussanalogyforFRPretrofittedURMwall.........................................................178

FigureC177:Plotshowingtherelationshipbetweenfeand..............................................1710

FigureC178:FRPretrofitforwallinExample15.1..................................................................1713

FigureC179:FRPretrofitforbuildinginExample15.2............................................................1714

FigureC181:NSMCFRPretrofitapplication..............................................................................183

FigureC182:Stressandstrainprofile........................................................................................184

FigureC184:Typicalwallfailuremechanisms...........................................................................187

FigureC183:Outofplanedesignprocedure.............................................................................187

FigureC185:Experimentalprogram..........................................................................................188

FigureC186:ExperimentalresultsofNSMCFRPwalltesting....................................................189

FigureC187:CFRPwallretrofitforExampleC18.7.2...............................................................1813

FigureC191:SequenceofFRSstrengtheningprocedures.........................................................193

FigureC192:InplaneFRSdesignprocedure.............................................................................194


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FigureC193:Distancesofxtandxcwithrespecttoaxialload...................................................196

FigureC194:OutofplaneFRSdesignprocedure.....................................................................197

FigureC195:NSMreinforcement..............................................................................................198

FigureC196:IllustrationofFRSeffectivedepth........................................................................198


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ListofTables

TableC11:NewZealandURMtypologies..................................................................................110

TableC12:NumberofURMbuildingsfromQVaccordingtoconstructiondecade..................111

TableC13:EstimatednumberofpotentiallyearthquakeproneandearthquakeriskURM

buildings......................................................................................................................................113

TableC21:Heighttothicknessratiocorrectionfactorformortarcompressivestrength...........22

TableC22:ParametersusedintheNZSEE(2006)guideline........................................................27

TableC23:Mohshardnessscale..................................................................................................29

TableC24:Mortardividingfactorsbasedonh/tratio...............................................................214

TableC25:Listoff'mvaluesfrompublications........................................................................223

TableC31:Fullscalediaphragmtestingsummary......................................................................38

TableC32:Examplebackboneforcedisplacementdatafortimehistoryanalysis...................310

TableC41:Modalparameterextractionmethods.......................................................................48

TableC42:Recommendedsuiteprofileforeachseismiczone.................................................415

TableC81:WallSchematics.........................................................................................................86

TableC82:WallSpecifications(Russelletal.2012).....................................................................86

TableC83:Comparisonofpredictedstrengthaccountingforandneglectingflanges(Russellet

al.2012).........................................................................................................................................86

TableC111:Estimatedwalldimensions.....................................................................................118

TableC112:%NBS.Zforslendernessratioof17.1,lowerstorey...............................................119

TableC113:%NBS.Zforslendernessratioof19.6,topstorey..................................................119

TableC114:Estimatedparapetdimensions.............................................................................1110

TableC115:Calculating%NBSforregionsexcludingnearfaulteffect....................................1110

TableC116:Calculating%NBSforregionsincludingnearfaulteffect.....................................1110

TableC117:Calculatingsheardemand....................................................................................1111

TableC118:Calculatingshearcapacity....................................................................................1111

TableC119:Oneleafwallassessment.....................................................................................1112

TableC1110:Oneleafwallassessment...................................................................................1113

TableC161:kValueforMomentCapacityEvaluationatHingeFormationLimitState............169

TableC162:PosttensionedWallDimensionsandPosttensioningDetails............................1613

TableC163:MasonryMaterials...............................................................................................1615


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TableC164:InputParameters.................................................................................................1615

TableC171:TypicalvaluesofFRPthickness,designrupturestrainandmodulusofelasticity...17

11

Table181:TypicalvaluesofmaterialpropertiesforCFRP........................................................183


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CommentarytoAssessmentandImprovementofUnreinforcedMasonryBuildingsfor

EarthquakeResistance

12/2011

C11

SectionC1HistoryandPrevalenceofUnreinforced

MasonryBuildingsinNewZealand

C1.1Introduction

NewZealandsmasonryconstructionheritageiscomparativelyyoung,spanningfrom1833until

the present time a period of less than 200 years. Furthermore, the majority of URM

construction inNewZealandoccurredbetween1880and1935.Consequently,astudyofNew

ZealandsURMbuildingstockhasanarrowscope incomparisonwith internationalnorms(see

for instanceBindaandSaisi (2005),Loureno (2006)andMagenes (2006)).Thiscomparatively

narrowtimeperiodhastheadvantageoffacilitatingthedocumentationandreportingofNew

ZealandURMconstructionpracticewithagreaterdegreeofaccuracythan isoftenpossible in

countrieswithanolderandmorediversehistoryofURMconstruction(Binda2006).

C1.2.1EarlySettlement

The first inhabitants of Aotearoa New Zealand were groups of Polynesian explorers who

discoveredandsettledtheislandsintheperiodA.D.8001000(King2003).Thesepeopledidnot

develop a tradition of building in masonry, but instead built using timber, earth and most

commonlyraupo (bulrush).Therearehowever,numerousstonerelatedarchaeologicalsites in

NewZealandattributedtoMaorisociety,themajorityofwhicharegardenwallsorassociated

withfortifications.ExamplesofMaoriconstructionareshowninFigureC11andFigureC12.

FigureC11:Raupowhare(house)atWairau

Pa,ca.1880(AlexanderTurnbullLibrary).

FigureC12:Raupoandtimberwharesofa

MaorivillageatMaketu,Kawhia,1895

(AlexanderTurnbullLibrary).

CaptainJamesCookanchoredoffthecoastofNewZealandon9October1769.Thiseventwas

followedbyagradualhaphazard increase inthepopulationofEuropeans inNewZealandover

the next 70 years, initially primarily associated with whaling, but also involving kauri timber

extractionandgoldmining.Jacobs(1985)reportsthattheEuropeanpopulationofNewZealand

in1830wasprobablyalittlemorethan300.By1839thenumberhadrisentopossibly2000,and


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SectionC1 HistoryandPrevalenceofUnreinforcedMasonryBuildingsinNewZealand

C12

atthebeginningofthe1850stherewas26,000EuropeansinNewZealand(seeFigureC13for

recordedpopulationdata).ThesefirstEuropeansettlersfoundthemselveswithouttheirfamiliar

building materials, so initially emulated the style and construction of Maori dwellings (Shaw

2003). For the most significant early buildings, such as churches and assembly buildings,

architectsfromAustraliaorEnglandwerecommissioned.

FigureC13: NewZealandtotalpopulationdata,18582007.

CaptainWilliamHobsonsarrivalin1840astheFirstGovernorGeneralofNewZealandmarked

thebeginningofNewZealand asaBritishcolony.Construction during the1840sto1860swas

primarilyoftimberforresidentialandsmallcommercialbuildings(seeFigureC14),butmasonry

buildingsdidbegintoappearclosetoharbours(seeFigureC15)andincitycentres.Inthelate

1850sChristchurchprosperedfromthewooltradeandthisallowedthetransitionfromwoodto

stoneandclaybrickmasonryforpublicbuildings.InChristchurchthetownhallwasbuiltinstone

in18621863,thefirststonebuildingofChristsCollegewasconstructedin1863,andthestone

Provincial Council Chambers was completed in 1864 (Wilson 1984). Oliver (2006) reports that

claybrickswerefirstmanufactured inAuckland in1852,withproductionofabout5,000bricks

perday.InAucklandcentralcitytheconstructionoftimberbuildingswasnotrestricteduntilthe

City of Auckland Building Act of 1856, with a fire in central Auckland in 1858 provided further

impetusforthetransitionfromtimbertoclaybrickmasonryconstruction.Similarfiresinother

city centres resulted in this transition from timber to masonry construction being mirrored

throughout New Zealand, suchas fires in inner city Christchurch in 1861, 1864,and 1866.The

centreofLytteltonwasalsodestroyedinafireonOctober24th,1870(ChristchurchCityLibraries

2006; Wilson 1984). The combustibility of timber structures prompted the move to URM

construction due to its fire resistant properties, with the high level of seismic activity in New

Zealandnotinfluencingthedecision,asthepoorlateralforceresistingpropertiesofURMwere

largelyunknownatthistimeofmassURMconstruction.Thefireproofnatureofmasonryledto

itbeingreadilyadoptedastheappropriatebuildingmaterialforhighimportancestructuressuch

asgovernmentbuildings,schools,andchurches.

0

1,000,000

2,000,000

3,000,000

4,000,000

5,000,000

1840 1860 1880 1900 1920 1940 1960 1980 2000 2020

Population

Year


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FigureC14:ShopsonQueenStreet,Auckland,

1859(AlexanderTurnbullLibrary).

FigureC15:QueenStreetandQueenStreet

Wharf,Auckland,in1882(AlexanderTurnbull

Library).

FigureC16andFigureC17 illustratetypicalURMconstructionscenes (althoughdated fromaslightlylaterperiod).InotherpartsofNewZealandtherewasamoreplentifulsupplyofnatural

stone,withNewZealandsearliestmasonrybuildinghavingbeenconstructedofstone in1833

(see Figure C18). Figure C19 shows an example of early rural construction in parts of New

Zealand where timber was scarce and natural stone was the primary construction material.

Evident in several of these figures is a predisposition to emulate mother country British

architecture. To some extent this emulation was due to the fact that there were very few

architects inNewZealandprior to1880,withmanydistinctivebuildingsdesignedbyoverseas

architects (Haarhoff2003). However Figure C110 shows that not all masonrybuildings were

well constructed. Hodgson (1992) reports that inferior materials and uncertain ground

conditionswerenotuncommon inbuildingprojectsof thisperiod.FigureC111 show thatby

1910 central Auckland was composed almost entirely of unreinforced masonry buildings.

Stacpoole and Beaven (1972) have similarly reported that Aucklandsearly wooden buildings

datingfromthe1840swerebadlyinneedofreplacementbythe1860s.

By1914 the centralareaofChristchurchhadbeen largely rebuilt, resulting inacity thatwas

interesting for its architectural variety, pleasing for its scale and distinctively New Zealand

(Wilson1984).FigureC112andFigureC113showphotosofhistoricalChristchurchfrom1885

and1910respectively.TwoofthemanyinfluentialarchitectsofChristchurchwereJ.C.Maddison

(18501923), whose design focus was inspired by the Italianate style, and J.J. Collins (18551933),whoinpartnershipwithR.D.Harman(18591927)chosebrickmasonryastheirmedium

forlargecommercialandinstitutionalbuildings.Bythe1920swoodenstructuresinChristchurch

wererare,andwereseenassmallirregularrelicsofthepast.

C1.3URMPerformanceinPastEarthquakes

C1.3.1Wairarapa,CanterburyandMurchisonEarthquakes

TheWairarapaearthquakeoccurredonTuesday23January1855,hadanestimatedmagnitude

of M8.2 (Grapes and Downes 1997) and is the largest earthquake to have occurred in New


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SectionC1HistoryandPrevalenceofUnreinforcedMasonryBuildingsinNewZealand

C14

ZealandsincethetimeofsystematicEuropeancolonisation(seeDowrickandRhoades(1998)for

a catalogue of major New Zealand earthquakes from 19011993). The shock was felt across

almostthewholecountry,washighlydestructiveinWellington,andalsocausedseveredamage

inWanganuiandKaikoura.Betweensevenandninepeoplewerekilled intheearthquake,and

fiveotherssustainedinjuriesthatrequiredhospitalisation.

FigureC16:Groupphotographofthe

constructionworkersthatbuilttheStratford

PublicHospitalduring19061907(Alexander

TurnbullLibrary).

FigureC17:Brickbuildingunder

construction,ca1920(AlexanderTurnbull

Library).

FigureC18:The1833StoneStoreatKerikeri

wasbuiltbytheChurchMissionarySociety.(A

PGodberCollection,AlexanderTurnbull

Library).

FigureC19:TwoChineseminersinfrontof

astonecottageincentralOtago,ca1860


TheM7.1NorthCanterburyearthquake in1888(Stirlingetal.2008)causedseveredamageto

buildingsmadeofcobandstonemasonryandcausedminordamagetobuildingsinChristchurch

(PapersPast 2010). A later earthquake in 1901 centred in Cheviot damaged the spire on the

CanterburyCathedralforthethirdtimeinitsshortlifeandledtoreconstructionofthespireintimber.FurtherdetailsarereportedinDizhuretal.(2010).


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FigureC110:Collapseofanewmasonry

auctionmarketbuilding,QueenStreet,


FigureC111:Lookingalongarowof

commercialbuildingsonQueenStreet,

Auckland,ca1910(AlexanderTurnbull

Library).

FigureC112:VictorianChristchurchin1885

(Coxhead1885)

FigureC113:Christchurchsfirst

skyscraper,photocirca1910

(BrittendenCollection1910)

TheM7.8earthquakethatstruckMurchisononthe17thofJune1929wasfeltthroughoutNew

Zealand(Dowrick1994).Fortunately,themost intenseshakingoccurred inamountainousand

denselywoodedareathatwassparselypopulated.Casualtieswerethereforecomparativelylight

andthedamagewasmostlyconfinedtothesurroundinglandscape,wheretheshakingtriggered

extensivelandslidesoverthousandsofsquarekilometres.Nonetheless,theshockimpactedwith

damagingintensitiesasfarawayasGreymouth,CapeFarewellandNelson(seeFigureC114and

FigureC115).FifteenpeoplewerekilledintheMurchisonearthquake.

C1.3.2The1931HawkesBayEarthquake,Napier

As reported above, itwas the combustibilityof timber construction thatprompted the focus

towardsbuilding inclaybrickunreinforcedmasonry,andoccasionally in stonemasonry.Early

earthquakes in theWellington region resulted in a slower adoptionofmasonry construction.

Thiscautionproved tobewelljustified.On themorningof3February1931 theHawkesBay

regionoftheeasternNorthIslandwasstruckbyanM7.8earthquakethatcompletelydestroyed

muchofthecityofNapier(seeFigureC116toFigureC118).Firessweptthroughthewreckage,

destroyingmuchofwhatwasleft.EightnursesdiedwhenthereinforcedconcreteNapiernurses

home collapsed, and perhaps the largest brick masonry building to collapse was the NapierAnglican Cathedral (see Figure C119). The shaking resulted in damage from Taupo to


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Wellington, and left 30,000 people homeless. The official death toll was 256, and the event

remainstheworstdisasterofanytypetooccuronNewZealandsoil(DalleyandMcLean2005;

Dowrick1998).

FigureC114:Generalstoredamagedbythe

1929Murchisonearthquake(Alexander

TurnbullLibrary).

FigureC115:Damagedbusinesspremises

aftertheearthquakeof17June1929


FigureC116:HastingsStreet,Napier,circa


FigureC117:ViewdownHastingsStreet,

Napierafterthe1931earthquake(Alexander

TurnbullLibrary).


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FigureC118:LookingoverNapieratthe

buildingsruinedbythe1931earthquakeandthe

fires(AlexanderTurnbullLibrary).

FigureC119:RuinsoftheNapierAnglican

Cathedralafterthe1931Napier

earthquake(AlexanderTurnbullLibrary).

Following thedemonstratedpoor seismic responseofURMbuildingsduring theHawkesBay

earthquaketherewasarapiddeclineintheuseofunreinforcedclaybrickmasonryconstruction,

which was eventually prohibited in 1965 (New Zealand Standards Institute 1965a). The

devastationof the1931HawkesBayearthquakeprompted theNewZealandGovernment to

bantheuseofunreinforcedmasonryonpublicbuildings (Oliver2006)andalsoprompted the

government todevelopanationalbuilding code, with the NewZealand Standards Institution

formed in 1932. This institution has survived to the present day, and is now referred to as

StandardsNewZealand.

C1.3.3GisborneandDarfieldEarthquakes

TheM6.82007Gisborneearthquake(FrancoisHoldenetal.2008)causeddamagetonumerous

unreinforcedmasonrybuildings,includingthecollapseof22parapets(DaveyandBlaikie2010).

Examplesofdamage toURMbuildings in the2007Gisborneearthquake are shown inFigure

C120andFigureC121.The2010Darfieldearthquakecausedextensivedamagetoanumberof

unreinforced masonry buildings (Dizhur et al. 2010; Ingham and Griffith 2011). Whilst this

damagetoimportantheritagebuildingswasthelargestnaturaldisastertooccurinNewZealand

since the1931HawkesBayearthquake, thedamagewas consistentwith projections for thescaleofthisearthquake,andindeedevengreaterdamagemighthavebeenexpected.Ingeneral,

the nature of damage was consistent with observations previously made on the seismic

performance of unreinforced masonry buildings in large earthquakes, with aspects such as

toppledchimneysandparapets,failureofgablesandpoorlysecuredfaceloadedwalls,and in

planedamagetomasonryframesallbeingextensivelydocumented(seeFigureC122andFigure

C123).


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FigureC120:Toppledparapetinthe2007

Gisborneearthquake.

FigureC121Outofplanefailureofagable

wallinthe2007Gisborneearthquake.

FigureC122:Outofplanewallfailureatthe

cornerofWorcesterandManchesterstreetsin

the2010Darfieldearthquake.

FigureC123:Outofplanewallfailureat118

ManchesterStreetinthe2010Darfield

earthquake.

C1.4NewZealandURMBuildingStock

InordertofosterageneralunderstandingofthearchitecturalcharacterofNewZealandsURM

building stock, a characterisation study was performed that identified the seven building

typologiesshowninFigureC124andreportedinTableC11.Theintentofthetypologystudyis

toassistininitialseismicassessment.FurtherdetailsarereportedinRussellandIngham(2010)

andRussellandIngham(2011).


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TypologyAbuilding onestoreyisolated TypologyBbuilding onestoreyrow

TypologyCbuilding twostoreyisolated TypologyDbuilding twostoreyrow

TypologyEbuilding three+storeyisolated TypologyFbuilding three+storeyrow

TypologyGbuilding religious TypologyGbuilding institutional

FigureC124:PhotographicexamplesofNewZealandURMtypologies


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TableC11:NewZealandURMtypologies

Type Description

Importance

level

(from

NZS1170.0)

Details

A Onestorey,

isolated

2,4 OnestoreyURMbuildings. Examplesinclude

conveniencestoresinsuburbanareas,andsmall

officesinaruraltown.

B Onestorey,

row

2,4 OnestoreyURMbuildingswithmultipleoccupancies,

joinedwithcommonwallsinarow. Typicalinmain

commercialdistricts,especiallyalongthemainstreet

inasmalltown.

C Twostorey,

isolated

2,4 TwostoreyURMbuildings,oftenwithanopenfront.

Examplesincludesmallcinemas,aprofessionaloffice

inaruraltownandpostoffices.

D Twostorey,

row

2,4 TwostoreyURMbuildingswithmultipleoccupancies,

joinedwithcommonwallsinarow. Typicalin

commercialdistricts.

E Three+

storey,

isolated

2,4 Three+storeyURMbuildings,forexampleoffice

buildingsinolderpartsofAucklandandWellington.

F Three+

storey,row

2,4 Three+storeyURMbuildingswithmultiple

occupancies,joinedwithcommonwallsinarow.

Typicalinindustrialdistricts,especiallyclosetoaport

(orhistoricport).

G Institutional,

Religious,

Industrial

2,3,4 Churches(withsteeples,belltowersetc),water

towers,chimneys,warehouses. Prevalent

throughoutNewZealand.

C1.4.1EstimationofURMPopulationandValue

In order to better understand the aggregated seismic performance of the nationwide URM

buildingstock,twoparallelexercises wereperformed toestimatethenumberanddistribution

ofURMbuildingsthroughoutNewZealand.ThefirstmethodinvolvedanassumptionthatURM

buildingswereconstructedapproximately inproportiontothenationalpopulationdistribution

oftheera,andthesecondmethodwasbasedupondatapurchasedfromQuotableValue(QV)

regardingtheexteriorbuildingfabricintheQVdatabase.Bothmethodsareestimatesonly,but


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provided similar findings, with further details reported in Russell and Ingham (2010). The QV

databasewasanalysedaccordingtoconstructiondate,buildingheightandfinancialvalue,with

TableC12reportingthedecadeinwhicheachURMbuildingwasconstructed.

TableC12:NumberofURMbuildingsfromQVaccordingto

constructiondecade

Decade URMBuildings

18701880 43

18801890 23

18901900 71

19001910 469

19101920 646

19201930 878

19301940 514

19401950 218

Mixed 726

Total 3590

TableC12clearlyshowsatrendwherethenumberofURMbuildingsinitiallyincreaseduntilthe

endofthe1920s,andsubsequentlydeclined.ThistrendfollowstheincreasingrateofEuropean

immigration and associated infrastructure development in New Zealand in the early 20th

Century (seeFigureC13),untilthe1931M7.8HawkesBayearthquake,after whichURMwas

nolongerconsideredafavourablebuildingmaterial.

A report prepared for the Department of Internal Affairs in 2002 (Hopkins 2002; Hopkins and

Stuart2003)showedthatthetotalfloorareaofbuildingsin32citiesandtownsthroughoutNew

Zealandwasapproximately27,200,000m2.ThetotalfloorareaofURMbuildingsextractedfrom

the QV database was approximately 2,100,000m2, suggesting that URM buildings make up

approximately 8% of the total New Zealand commercial building stock in terms of floor area.

FromtheQVdatabaseitwasalsopossibletoestablishthat86%ofthenationwideURMbuilding

stock is either a one or two storey building, and that the aggregated value of these buildings

(based on an assessment period between July 2005 and September 2008) is approximately

NZ$1.5billion. However, it must berecognisedthatmanybuildings havea worth greater than


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theirfinancialvaluation,includinganarchitectural,historicorheritagevaluetothecommunity,

whichcanbedifficulttoquantify(Goodwin2008;Goodwinetal.2009).

C1.4.2EstimatedVulnerabilityofURMBuildings

Following determination of the number of URM buildings and their approximate regional

distribution, an analysis was performed to estimate the expected vulnerability of the URM

buildingpopulation.ThedetailsoftheanalysisarereportedinRussellandIngham(2010),with

the results reported in FigureC125 and inTableC13. It is recognised that the analysiswas

essentially qualitative in nature and can be expected to overestimate the number of poorly

performing URM buildings, primarily because of the conservative nature of the IEP.

Nevertheless, as an informative estimate of the nature of the vulnerability of New Zealands

URMbuildingstock,thisanalysis isconsideredrobust.Additionally,thisanalysisdoesnottake

into account the number of buildings which have already been seismically improved, which

Thornton (2010)notes isnot insignificant. Data that became available followingdamage to

URM buildings in the 2010 Darfield earthquake (reported in Ingham and Griffith (2011))

indicatedgeneralsupportforthisanalysis,althoughitwasevidentfollowingtheearthquakethat

theanalysispresentedinFigureC125underestimatedthetotalnumberofURMbuildingsinthe

Canterburyregion(seeDizhuretal.(2010)).

FigureC125:Estimated%NBSofURMbuildingsinProvincesthroughoutNewZealand


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TableC13:EstimatednumberofpotentiallyearthquakeproneandearthquakeriskURM

buildings

Province Potentiallyearthquake

prone

Potentially

earthquakerisk

Unlikelytobe

significantrisk

Auckland 41 3% 628 31% 357 74%

Taranaki 59 4% 105 5% 0 0%

HawkesBay 85 6% 1 0% 0 0%

Wellington 622 45% 55 3% 0 0%

Marlborough 42 3% 5 0% 0 0%

Nelson 94 7% 37 2% 0 0%

Westland 39 3% 2 0% 0 0%

Canterbury 338 24% 513 26% 0 0%

Otagoand

Southland66 5% 664 33% 126 26%

Total 1386 36% 2010 52% 483 12%

C1.5NewZealandBuildingCodesPertainingtoURMConstruction

The Great Depression in the 1930s and the outbreak of World War II significantly slowed

progressintheconstructionsector,andfewlargebuildingsofanymaterialwereconstructedin

the period between 1935 and 1955 (Megget 2006; Stacpoole and Beaven 1972). Equally

important in the history of URM buildings in New Zealand was the 1931 M7.8 Hawkes Bay

earthquake, and the changes in building provisions which it precipitated. Later in 1931, in

response to that earthquake, the Building Regulations Committee presented a report to theParliamentofNewZealandentitledDraftGeneralBuildingByLaw(Cull1931),whichwasthe

firststeptowardsrequiringseismicprovisionsinthedesignandconstructionofnewbuildings.In

1935, this report evolved into NZSS no. 95, published by the newly formed New Zealand

Standards Institute, and required a horizontal acceleration for design of 0.1g, and this

requirementappliedtothewholeofNewZealand(NewZealandStandardsInstitute1935).NZSS

no. 95 also suggested that buildings for public gatherings should have frames constructed of

reinforced concrete or steel. The ByLaw was not enforceable, but it is understoodthat it was

widely used especially in the larger centres of Auckland, Napier, Wellington, Christchurch and

Dunedin(Megget2006).TheprovisionsofNZSSno.95wereconfinedtonewbuildingsonly,but

the draft report acknowledged that strengthening of existing buildings should also be


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considered,andthatalterationstoexistingbuildingswererequiredtocomply(Davenport2004).

In1939and1955neweditionsofthisByLawwerepublished,andapartfromsuggestingin1955

thattheseismiccoefficientvarylinearlyfromzeroatthebaseto0.12atthetopofthebuilding

(formerly the seismic coefficient was uniform up the height of the building), there were few

significantchanges(Beattieetal.2008).Itwasnotuntil1965thatmuchoftherecentresearchat the time into seismic design was incorporated into legislation. The New Zealand Standard

Model Building ByLaw NZSS 1900 Chapter 8:1965 explicitly prohibited the use of URM: (a) in

ZoneA;(b)ofmorethanonestoreyor15ft(4.6m)eavesheightinZoneB;(c)ofmorethantwo

storeysor25ft(7.6m)eavesheightinZoneC.Thesezonesrefertotheseismiczonationatthe

time,whichhavesubsequentlychangedandevolved.ZoneAconsistedofregionsofthehighest

seismicriskandZoneCconsistedofregionsofthe lowestseismicrisk(NewZealandStandards

Institute1965b).Again,theprovisionsofthisByLawdidnotapplyautomaticallyandhadtobe

adoptedbylocalauthorities.

The1965coderequiredthatbuildingsbedesignedandbuiltwithadequateductility,althoughfurtherdetailswerenotgiven.Thenextversionofthe loadingscodewaspublished in1976as

NZS4203(StandardsAssociationofNewZealand1976),andwasamajoradvanceonthe1965

code.Most importantly, the1976 loadingscodewasused inconjunctionwithrevisedmaterial

codes: steel, reinforced concrete, timber and reinforced masonry, which all required specific

detailingforductility.Thusafterthepublicationofthiscodein1976,unreinforcedmasonrywas

explicitlyprohibitedasabuildingmaterialthroughoutthewholeofNewZealand.

The use of URM was implicitly discouraged through legislation from as early as 1935, and

although it was still allowed in some forms after 1965, observations of existing building stock

show its minimal use from 1935 onwards, especially for larger buildings. This is thought to be

significantlyattributabletotheexceptionallyrigorousqualityofdesignandconstructionbythe

MinistryofWorksatthetime(Johnson1963;Megget2006).AlthoughtwostoreyURMbuildings

werepermittedinAuckland(ZoneC)after1965,onlythreeexistingURMbuildings inAuckland

City constructed after 1940 have been identified. All three are single storey and they were

constructedin1950,1953and1955.

C1.5.1ProvisionsfortheSeismicUpgradeofExistingBuildings

As building codes were being developed for the design of new buildings, attention was also

giventotheperformanceofexistingbuildingsinearthquakes.Thefirsttimethiswasaddressed

in legislation was Amendment 301A to the 1968 Municipal Corporations Act (New Zealand

Parliament 1968). This Act allowed territorial authorities, usually being boroughs, cities or

district councils, to categorise themselves as earthquake risk areas and thus to apply to the

government to take up powers to classify earthquake prone buildings and require owners to

reduceorremovethedanger.Buildings(orpartsthereof)ofhighearthquakeriskweredefined

as being those of unreinforced concrete or unreinforced masonry with insufficient capacity to

resistearthquakeforcesthatwere50%ofthe magnitudeofthoseforcesdefined byNZS 1900

Chapter8:1965.Ifthebuildingwasassessedasbeingpotentiallydangerousinanearthquake,

thecouncilcouldthenrequiretheownerofthebuildingwithinthetimespecifiedinthenotice

toremovethedanger,eitherbysecuringthebuildingtothesatisfactionofthecouncil,orifthe


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council so required, by demolishing the building. Most major cities and towns took up the

legislation,andasanindicationoftheeffectofthisAct,between1968and2003WellingtonCity

Council achieved strengthening or demolition of 500 out of 700 buildings identified as

earthquakeprone(Hopkinsetal.2008).

AucklandCityCouncil,inspiteofhavingalowseismicity,tookastronginterestinthelegislation

andthisledtoconsiderableactivityinstrengtheningbuildings(Boardman1983).InChristchurch,

a moderately high seismic zone, the City Council implemented the legislation, but adopted a

more passive approach, generally waiting for significant developments to trigger the

requirements.InDunedin,nowseentobeoflowseismicrisk,littlewasdoneinresponsetothe

1968 legislation although strengthening of schools, public buildings and some commercial

premiseswasachieved.Asaresult,DunedinhasahighpercentageofURMbuildingscompared

withmanyothercitiesinNewZealand(Hopkins2009).Megget(2006)andThornton(2010)state

thatmuchofthestrengtheninginWellingtonwasaccomplishedwithextrashearwalls,diagonal

bracingorbuttressingandthetyingofstructuralfloorsandwallstogether,andthatmanybrittlehazards such as parapets and clock towers had been removed after the two damaging 1942

SouthWairarapaearthquakes(M7.0&M7.1)whichwerefeltstronglyinWellington.Hopkinset

al.(2008)notedthattherewascriticismatthelossofmanyolderheritagebuildingsandatthe

useofintrusiveretrofittingmeasureswhichwerenotharmoniouswiththearchitecturalfabricof

thebuilding(McClean2009).Atthesametime,thisdidprovideanopportunityinmanycasesfor

thelandonwhichtheoldbuildingwassituatedtobebetterutilisedwithnew,largerandmore

efficientlydesignedstructures.

Amajordrawbackofthe1968 legislation,whichendureduntil2004,surviving intactwiththe

passageoftheBuildingAct 1991,wasthatthedefinitionof anearthquake pronebuildingand

therequiredleveltowhichsuchbuildingsshouldbeimprovedremainedtiedtothe1965code.

Mostterritorialauthoritiescalledforstrengtheningtoonehalfortwothirdsofthe1965code,

andmanybuildingswhichwerestrengthenedto these requirementsweresubsequentlyfound

tofallwellshortoftherequirementsoflaterdesignstandardsfornewbuildings(Hopkinsetal.

2008). (Wellington City Council found that in January 2008, of 97 buildings which had been

previouslystrengthened,61(63%)weresubsequentlyidentifiedaspotentiallyearthquakeprone

(Bothara et al. 2008; Stevens and Wheeler 2008)). This situation was recognised by the New

Zealand Society for Earthquake Engineering (NZSEE), who were also concerned about the

performance of more modern buildings, particularly after the observed poor performance ofsimilarlyagedbuildings inearthquakesinNorthridge,California(1994)andKobe,Japan(1995).

NZSEEpushedfornew,moreuptodateandwideranginglegislation.Thispushwassupported

by the Building Industry Authority, later to become part of the Department of Building and

Housing, and a new Building Act came into effect in August 2004 (New Zealand Parliament

2004). This brought innewchanges as towhat constitutedan EarthquakeProneBuilding. In

particular, the definition of an earthquake prone building was tied to the current design

standardofthetime,andnolongertothedesignstandardofanyparticularyear.Thelegislation

allowedanyterritorialauthoritythat issatisfiedthatabuilding isearthquakepronetorequire

theownertotakeactiontoreduceorremovethedanger.Eachterritorialauthoritywasrequired

tohaveapolicyonearthquakepronebuildings,andtoconsultpubliclyonthispolicybeforeits


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adoption.Policieswererequiredtoaddresstheapproachandprioritiesandtostatewhatspecial

provisions would be made for heritage buildings. The 2004 legislation applied to all types of

buildings except small residential ones, (residential buildings were excluded unless they

comprised2ormorestoreysandcontained3ormorehouseholdunits).

Assoonasthe1968legislationcameintoeffecttoattempttomitigatetheeffectsofearthquake

pronebuildings,theNewZealandNationalSocietyforEarthquakeEngineeringsetupasteering

committeetoprovideacodeofpracticeinanefforttoassistlocalauthoritiestoimplementthe

legislation. Since the first draft code of practice published by the NZNSEE (1972), several

successive publications have been produced, each extending on the previous version. These

guidelineshavebeen instrumental inhelpingengineersandterritorialauthoritiestoassessthe

expected seismic performance of existing buildings consistent with the requirements of the

legislation.Guidelinesforassessingandupgradingearthquakeriskbuildingswerepublishedasa

bulletinarticle in1972(NZNSEE1972)andthenseparatelypublishedthefollowingyear,which

became colloquially known as the Brown Book (NZNSEE 1973). This document providedguidelines for surveying earthquake risk buildings and for the identification of particularly

hazardous buildings and features, and was found to be helpful in many respects. It did not

establish or recommend strength levels to which earthquake prone buildings should be

upgraded,andthusstandardsvariedfromoneareatoanother.Itwasimplicitthatstrengthening

be to more than half the standard required in Chapter8 of the1965NZSS Model Building By

Law.

In1982,NZSEEestablishedastudygrouptoexamineandrationalisetheuseoftheseguidelines

and to produce further guidelines and recommendations. This activity culminated in the

publicationin1985ofwhatbecameknownasthe1985RedBook(NZNSEE1985).Again,this

document was primarily of a technical nature and the responsibilities of what to do with

buildingsstillrestedwithlocalauthorities.Thepublicationwasintendedtopromoteaconsistent

approach throughout New Zealand for the strengthening of earthquake risk buildings and

includedarecommendedleveltowhichbuildingsshouldbestrengthenedplusthetimescaleto

complete the requirements. The basic objective was to establish a reasonably consistent

reduction of the overall risk to life which the countrys stock of earthquake risk buildings

represented.Basedonoverseasexperiences,particularlyinLosAngelesinSouthernCalifornia,a

philosophy was accepted of providing owners of earthquake risk buildings with the option of

interim securing to gain limited extension of useful life, after which the building should bestrengthenedtoprovideindefinitefuturelife.Thedesignofinterimsecuringsystemswastobe

basedonminimumseismiccoefficientswhichrepresentedtwothirdsofthosespecifiedinNZSS

1900, Chapter 8 (New Zealand Standards Institute 1965b). For permanent strengthening

measures, it was recommended that the building be strengthened to the standard of a new

building, but with the design lateral forces reduced depending on the occupancy classification

andtypeofstrengtheningsystem.Thispublicationwaswidelyusedbyterritorialauthoritiesand

designers.

In1992theNZNSEEagainsetupastudygrouptoreviewthe1985publication,andthisresulted

in another publication, which similarly became colloquially known as the 1995 Red Book(NZNSEE1995).Thisdocumentextendedtheapproachandcontentofitspredecessorandtook


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into account the changing circumstances, technical developments and improved knowledge of

the behaviour ofURM buildings in earthquakes. In particular, earthquakerisk buildings in that

document were taken to include all unreinforced masonry buildings, and notjust those which

weredefinedasearthquakeproneintermsoftheBuildingActofthetime,whichstillreferred

backtothe1965code.Anotherkeydifferencefromthe1985RedBookwasthatasinglestageapproach to strengthening was suggested, in contrast to the two stage securing and

strengtheningprocedureofthe1985document.Theguidelinesalsohighlightedthedifferences

in analysis for unsecured buildings in comparison to a building which has positive connections

between floor, roof and wall elements, and cantilever elements secured or removed. Greater

emphasis was placed on the assessment of the likely performance of URM buildings in their

original form and with interim securing only in place, as distinct from the performance of the

building with any strengthening work which was subsequently found to be necessary.

Furthermore, material strengths were given in ultimate limit state format. Historic or heritage

buildingswerenotgivenanyspecificorseparatetreatment,andtheguidelinesstatedthatthe

issuesofriskversusthepracticalitiesofstrengtheningassociatedwithhistoricbuildingsrequire

evaluationonacasebycasebasis.Theprincipalproblemwithsuchbuildingsisthatthegreater

theleveloflateralforcesthatisspecifiedforstrengthening,thegreatertheriskofdamagingthe

fabricthatistobepreserved(NZNSEE1995).

After the introduction of a new Building Act in 2004 (New Zealand Parliament 2004) the

Department of Building and Housing supported NZSEE in producing a set of guidelines,

Assessment and Improvement of the Structural Performance of Buildings in Earthquakes

(NZSEE2006).Thiswasamajorreviewandextensionofpreviousguidelines,toaccountforthe

widerscopeoftheproposednewlegislation.PriortoenactingTheBuildingAct2004,thetermearthquakeriskbuildingrelatedonlytoURMbuildings,butnowanearthquakepronebuilding

couldbeofanymaterial;steel,concrete,timberormasonry.Thelevelofriskposedbybuildings

constructedasrecentlyasthe1970swasmorewidelyappreciated,inparticulartheinadequate

performance of reinforced concrete structures due to deficient detailing. Definitions of

earthquakeproneandearthquakeriskalsochanged.Essentially,earthquakepronebuildings

were defined as those with onethird or less of the capacity of a new building. While The

Building Act itself still focussed on buildings of high risk (earthquake prone buildings), NZSEE

considered earthquake risk buildings to be any building which is not capable of meeting the

performance objectives and requirements set out in its guidelines, and earthquake prone

buildings formed a subset of this. Moreover, NZSEE expressed a philosophical change, in

acknowledgmentofthewiderangeofoptionsforimprovingtheperformanceofstructuresthat

are found to have high earthquake risk. Some of these options involve only the removal or

separationofcomponents,andothersaffectarelativelysmallnumberofmembers.Inlinewith

performancebaseddesignthinking,thetermstrengtheningwasreplacedwithimprovingthe

structuralperformanceof,highlightingthefactthatsuchsolutionsasbase isolationwerenot

strengtheningbutwereaneffectivewayofimprovingstructuralperformance.

The 2006 guidelines (NZSEE 2006) provided both an initial evaluation procedure (IEP) and a

detailed analysis procedure. The IEP can be used for a quick and preliminary evaluation of

existingbuildings,andtakes intoaccountthebuildingform,naturalperiodofvibration,critical


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structural weaknesses (vertical irregularity, horizontal irregularity, short columns and potential

for buildingtobuilding impact) and the design era of the building. Based on this analysis, if a

territorial authority determines a building to be earthquake prone, the owner may then be

requiredtotakeactiontoreduceorremovethedanger,dependingontheterritorialauthoritys

policy and associated timeline. The level required to reduce or remove the danger is notspecified in The Building Act or its associated regulations. The Department of Building and

Housing suggested that territorial authorities adopt as part of their policies that buildings be

improvedtoalevelasnearasisreasonablypracticaltothatofanewbuilding.Mostterritorial

authorities took the view that they could not require strengthening beyond onethird of new

buildingstandard,butasignificantnumberincludedrequirementstostrengthentotwothirdsof

new building standard, in line with NZSEE recommendations. In developing policies on

earthquake prone buildings, most territorial authorities recognised the need for special

treatmentanddialoguewithownerswhenheritagebuildingswereaffected.Itisbelievedbythe

DepartmentofBuildingandHousingthatthelegislationhasrequiredeachl

commentary to assessment and improvement of unreinforced masonry buildings for earthquake resistance

Documents