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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
TurnbullLibrary)............................................................................................................................14
FigureC110:Collapseofanewmasonryauctionmarketbuilding,QueenStreet,1865
(AlexanderTurnbullLibrary).........................................................................................................15
FigureC111:LookingalongarowofcommercialbuildingsonQueenStreet,Auckland,ca1910
(AlexanderTurnbullLibrary).........................................................................................................15
FigureC112:VictorianChristchurchin1885(Coxhead1885).....................................................15
FigureC113:Christchurchsfirstskyscraper,photocirca1910(BrittendenCollection1910)..15
FigureC114:Generalstoredamagedbythe1929Murchisonearthquake(AlexanderTurnbull
Library)..........................................................................................................................................16
FigureC115:Damagedbusinesspremisesaftertheearthquakeof17June1929(Alexander
TurnbullLibrary)............................................................................................................................16
FigureC116:HastingsStreet,Napier,circa1914(AlexanderTurnbullLibrary)..........................16
FigureC117:ViewdownHastingsStreet,Napierafterthe1931earthquake(AlexanderTurnbull
Library)..........................................................................................................................................16
FigureC118:LookingoverNapieratthebuildingsruinedbythe1931earthquakeandthefires
(AlexanderTurnbullLibrary).........................................................................................................17
FigureC119:RuinsoftheNapierAnglicanCathedralafterthe1931Napierearthquake
(AlexanderTurnbullLibrary).........................................................................................................17
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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EarthquakeResistance
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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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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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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
(AlexanderTurnbullLibrary).
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,
1865(AlexanderTurnbullLibrary).
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
(AlexanderTurnbullLibrary).
FigureC116:HastingsStreet,Napier,circa
1914(AlexanderTurnbullLibrary).
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