austral deck - bbp.style · table 8 – as3600-2009 table 4.10.3.3 - concrete cover 30 list of...
TRANSCRIPT
AUSTRAL PRECAST
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Austral Deck TECHNICAL GUIDE
CONTENTSbuild faster, build smarter, build better
1. Introduction
1.1 Austral Deck – Overview 6
1.2FeaturesandBenefits 8
1.3 Applications 9
2. Properties of Austral Deck
2.1 Standard Austral Deck Design Thicknesses, 10
Span Table and Graph
2.2 Calculation of Austral Deck Weight Reduction 12
2.2.1 Basic Self-Weight Calculations 12
2.2.2RefinementstotheSelf-Weight 12
2.2.3Multi-SpanWeightCalculationExample 13
2.2.4 Calculations Using Software 13
2.3 Calculation of Austral Deck Stiffness 15
2.3.1 Calculation of the Neutral Axis – 15
Elastic Section
2.3.2CalculationoftheMomentofInertia 15
2.3.3 Calculation of Elastic Stiffness Allowing for 16
Joints
3. Modelling Austral Deck
3.1 Design Principles 17
3.2 General Modelling 17
3.2.1OutputsfromModelling 17
3.2.2CodeCompliance 17
3.3UsingRamConcept 17
3.3.1AdjustmentforStructuralWeight 18
3.3.2 Average Slab Thickness 19
3.3.3 Reduced Concrete Stiffness 19
3.3.4IsotropicvsOrthotropicStiffness 20
3.3.5 Austral Deck and Orthotropic Stiffness 20
3.3.6 Orthotropic Stiffness and Australia Code
Compliance 20
3.3.7 Austral Deck and RAM Concept Design Strips 21
3.3.8RAMConceptandAS3600-2009 21
Implementation
3.3.9AustralDeckandRAMConceptDeflection 21
Analysis
3.3.10ExampleAustralDeckLoadHistorySettings 22
3.4AustralDeckDesignStripLayoutinRAMConcept 23
3.4.1ExampleDesign 23
3.4.2 Flat Plate 24
3.4.3BandedSlab 28
4. Austral Deck and AS3600 Detailing Requirements
4.1 Concrete Cover 30
4.1.1CodeRequirements 30
4.2DuctilityRequirementsinFlexuralReinforcement 31
4.3ReinforcementLayingSequence 31
4.4DetailingofSpanDirectionReinforcement 32
4.4.1 End Supports 32
4.4.2InternalSupports 32
4.4.3NegativeReinforcement 32
4.5DetailingofCrossDirectionReinforcement 32
4.6 Calculation of Splice Bars 33
4.7 Punching Shear 33
4.7.1GeneralDesignIssues 33
4.7.2PunchingShearReinforcementand 33
Austral Deck
4.7.3 Basic Punching Shear Checks 33
4.7.4 Punching Shear Using Rebar Trusses 34
4.7.5 Alternatives for Punching Shear 34
4.8LongitudinalShear 35
5. Austral Deck Design as Formwork
5.1Stageone:Designasformwork 36
5.2DesignCriteriaandSpecifications 37
5.2.1 Strength 37
5.2.2 Stiffness 37
5.2.3 Surface Finish 37
5.2.4 Panel Capacity 37
5.2.5MaximumSpan 37
5.2.6StackedMaterials 38
5.2.7Assumptions 38
5.3 Panel Properties 39
5.3.1ConstructionLoads 39
5.3.2LoadCombinations 39
5.3.3DesignLoad 39
5.3.4 Truss Properties 39
5.3.5 Top Chord 39
5.3.6BottomChord 39
5.3.7DiagonalLacing 39
5.3.8Mesh 39
5.3.9 Capacity Calculations 40
5.3.10TopChordCompression 40
5.3.11 Top Chord Tension 40
5.3.12BottomChordCompression 40
5.3.13BottomChordTension 40
5.4 Panel Properties 39
5.4.1BottomChordTension 40
5.4.2DiagonbalLacingCompression 41
5.4.3ConcretePanelCompression 41
5.3.4 Control for Concrete Tensile Strength 41
5.3.5 Crack Control for Flexure 41
5.3.6Deflection 42
5.3.7MaximumScansSummary 42
5.3.8SingleSpan 43
5.3.9 Two Span 43
6. Example Models and Calculations
6.1SensitivityAnalysisofTwo-WaySlabs–Example1 44
6.2 Worked Calculations 46
6.1.1 Strip 1 – Vertical Span 47
6.1.1Strip2–HorizontalSpan 48
6.1.3CheckonColumnStripWidth 48
6.1.4CheckonSecondaryMomentDirection 48
6.1.5 Check on Punching Shear 49
7. Fire and Thermal Resistance
7.1 Fire Resistance Period 51
7.1.1AustralDeckProfile 51
7.1.2ThermalResistance 51
7.1.3DefinitionsandReferences 51
8. Typical Installation Details
8.1TypicalWallConnection–EndSupport 52
8.1.1EndSupporttoExternalPrecastWall-Option1 52
8.1.2EndSupporttoExternalPrecastWall-Option253
8.1.3EndSupporttoInternalPrecastWall 53
8.2TypicalWallConnection–LongitudinalSide 54
8.2.1LongitudeSidetoExternalPrecastWall 54
8.2.2SideJointDetails 54
8.3TypicalWallConnection–InternalPrecastWalland 54
Double Wall
8.3.1EndSupport–InternalPrecastWallUnder 54
8.3.2MidSpan–InternalPrecastWallAbove 55
8.3.3EndSupport–DoubleWallConnection 55
8.4TypicalBeamConfiguration 55
8.4.1BeamReinforcementwithinSlabThickness 55
8.4.2PrecastBeam 56
8.4.3BandBeamformedbyAustralDeck 56
8.5BalconyandCantileverArrangement 57
8.5.1BalconyandCantileverArrangement 57
8.5.2ExternalPrecastWallwithBalcony 57
8.6ProposedProppingArrangement 58
LIST OF FIGURES
Figure 1 – Typical Austral Deck Cross Section 7
Figure2–Integrationwithsteelframedsructure 8
Figure 3 – Austral Deck Cross Sections 12
Figure4–PlanofAustralDeckAroundColumn 13
Figure5–TypicalMultipleSpanAustralDeckLayout 14
Figure 6 – Elastic Analysis of Panel Joints 16
Figure7–RAMConceptMenu 18
Figure8–SlabpropertiesshowingAustralDeck 19
concretemixandcustomreducedstiffness
Figure9–Designstripdistributionfrom 20
AS3600-2009 Table 6.9.5.3
Figure 10 – RAM Concept load history options 21
Figure11–RAMConceptstriplayoutexample 23
Figure 12 – RAM Concept strip layout - 3D render 23
Figure13–Examplemodelshowingmesharealayouts 24
Figure14–Exampleplanklayout#1 25
Figure15–Exampleplanklayout#2 25
Figure16–Latitudeandlongitudedesignstrips 26
Figure17–Longitudinalsectionsgeneratedfrom 27
design strips
Figure18–Bandedslablayout 28
Figure19–Bandedslab3Drender(viewedfrombelow) 28
Figure20–Longitudestriplayoutforbandedslab 29
Figure21–Bandedslabdeflectionprofile 29
Figure22–CoverrequirementsforAustralDeckplanks 30
Figure23–Reinforcementbarlayingsequence 31
Figure 24 – Typical internal support splice bar locations 32
Figure 25 – Splice bar calculation of forces 33
Figure 26 – Punching Shear Setback 34
Figure27–InteriorSupportDuringConstruction 36
Figure28–Longterm(30year)deflectionfor100%, 44
75%and50%secondarystiffness
Figure29–Primarypositivemoment(aboutRaxis) 45
Figure30–Primarynegativemoment(aboutRaxis) 45
Figure31–Secondarypositivemoment(aboutSaxis) 45
Figure32–Secondarynegativemoment(aboutSaxis) 45
Figure33–ExampleSlab 46
Figure34–ExampleSlab 47
Figure35–AustralDecksideprofile 51
Figure 36 – Effective thickness for FRP ccalculation Austral 51
AustralDeckprofile
Figure 37 – End Support to External Precast Wall - Option 1 52
Figure38–EndSupporttoExternalPrecastWall-Option253
Figure39–EndSupporttoInternalPrecastWall 53
Figure40–LongitudeSidetoExternalPrecastWall 54
Figure41–EndSupport–InternalPrecastWallUnder 54
Figure42–MidSpan–InternalPrecastWallAbove 55
Figure 43 – End Support – Double Wall Connection 55
Figure44–BeamReinforcementwithinSlabThickness 55
Figure45–PrecastBeam 56
Figure46–BandBeamformedbyAustralDeck 56
Figure47–BalconyandCantileverArrangement 57
Figure48–ExternalPrecastWallwithBalcony 57
Figure49–ProposedProppingArrangement 58
LIST OF TABLES
Table 1 – Standard Austral Deck Slab Thicknesses 10
and Design Properties
Table 2 – Span to Deck ratios for residential application 11
Table3–RAMConceptConcreteMixProperties 18
Table 4 – Reduced Austral Deck densities for regular 19
andbathroomslabareas
Table5–Designcolumnandinteriorstripsas 20
definedbyAS3600-2009Section6.1
Table 6 – Typical load history settings for a 22
residential Austral Deck slab
Table 7 – AS3600-2009, Table 4.3 - Concrete 30
ExposureClassification
Table8–AS3600-2009Table4.10.3.3-ConcreteCover 30
LIST OF CHARTS
Chart 1 – Span Chart Guide 11
Chart2–Maximumdistancebetweensupportsfor 43
single span
Chart3–Maximumdistancebetweensupportsfor 43
multispan
Chart 4 –Fire Resistance Period 11
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Austral Deck TECHNICAL GUIDE
Theinformationcontainedinthisdocumentisprovided
asageneralguideonlyanddoesnotreplacetheneedforthespecificationto
bereviewedandcheckedbyaqualifiedpersoninthefieldofconcrete,
energy,buildingconstruction,sound,design,servicesand/orfire.
Thismaterialhasbeenpreparedinthecontextofrelevant
AustralianStandards,theNationalConstructionCode(NCC)andthe
BuildingCodeofAustralia(BCA).Usersshouldmakethemselvesawareof
anyrecentchangestothesedocumentsreferredtotherein
andtolocalvariationsorrequirements.
Austral Precast has dedicated engineering services available for project
assistance.Weareabletoprovidedesignsupportforengineerstodetermine
thebestwaytospecifyanddocumentAustralDeck.
Ourtechnicalexpertscanidentifythemostefficientpanelgeometrymeeting
projectrequirements,specificationsandinstallationprocess.
Austral Precast offers fully detailed shop drawings as part of the
Austral Deck supply.
Itistheclient’sdesignerwhoisresponsibletodesignandcertifythe
concreteslab,theentirestructureandcertifythepaneldesignfortemporary
propping and construction loads.
AUSTRAL DECKdesign for construction, loading,
permanent formwork, span capacity and final in service slab
AUSTRAL PRECAST
AUSTRAL PRECAST
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WelcometoAustralDeck,aninnovative,costeffectiveand
timesavingprecastconcreteflooringsolution,designedto
provideaonewayandtwo-wayspanningconcretefloorslab
andformworksolutioninone.
AustralDeckcombinesfeaturesdevelopedfrommanyyearsof
research,developmentandconstructionprojectstoprovidea
flexiblesolutionthatenablesengineers,architectsand
builderstounderstandandusethesolutionasseamlesslyasif
theyweredesigningatraditionalconcreteframedbuilding.
TheGuideaimstoenableusersto:
•AchieveapreliminaryunderstandingoftheAustralDeck
solution,spans,costsandlimitations
• Undertake designs and understand the theory behind their
implementation
• Understand the way that Austral Deck is constructed, and
plan accordingly.
1.1 Austral Deck – OverviewAustralDeckisbasedaroundasmallnumberofkey
components,thatcombinetoformafullybonded,concrete
slab.
Thecomponentscombinethestrengths,savingsandbenefits
ofprecastconcretewiththeflexibilityandsimplicityof
traditionalin-situformed,pouredandfinishedfloorslabs.
The solution can be broken down into the following key
components(Figure1):
1. A thin precast concrete “Austral Deck panel” providing a
Class2bottomsoffitfinishwhilstservingasformwork.
2.Reinforcementbar(rebar)andmeshcastintotheAustral
Deck panel, providing concrete spanning capability and
contributestoslabreinforcement.
3.Triangularsteellatticegirder“trusses”madefromwelded
rebar,providingtemporarystiffnessfortransportand
installation.Theyprovidepermanentshearflowtransfer
capability.
4.Voidformers,reducingtheweightoftheoverallslaband
increasingtheefficiencyoftheconcretesection.
5.On-siteinstallationoftopreinforcementandsplicebars,
providing easy access to cast in services whilst achieving
rapidsteelfixingtimeframesonsite.
6.In-situpouredconcretetopping.
1. INTRODUCTION
01 Austral Deck
02 Steelreinforcementifspecified03 Steel lattice girder
04SteelmeshcastedintheAustralDeck05Voidformers06In-situconcretetopping07 Slab thickness
Figure 1 – Typical Austral Deck Cross Section
07
06
01
0304
02
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Austral Deck TECHNICAL GUIDE
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AUSTRAL PRECAST
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Austral Deck TECHNICAL GUIDE
1.2 Features and BenefitsAustral Deck is easy to design with and fast to install, saving
timeandmoneyacrosstheconstructionlifecycle.
Aflexibleandadaptableformwork,AustralDeckintegrates
well with Austral Precast walling solutions, covering the
entire structure including cantilevers and balconies.
A unique flooring solution
•AnAustralDeckpanelispartofacompositefloorsolution
thatprovidesrigidformworkthatbecomespartofthefinal
structure. During construction the panel can stand
constructionloadsandbeusedasaplatformforworkersand
materials.
•Aneffectivewaytomaintainthestructuralintegrityofa
monolithicslab.
•Compositeplatformsandshearconnectionpanelscanbe
constructed easily with partial or full-length gaps or pockets
ofconcretevoids.Thegapswillbelocatedtoaccommodate
structuralbeamconfigurations.Thisallowsforthe
placementoftheAustralDeckdirectlyoverprecast,cast
in-situconcreteorsteelbeams.Trussesandsteel
reinforcementcanremainuninterruptedthroughthesegaps
for structural continuity. – Figure 2.
•Thispermanentformworksolutionhasbeenapprovedby
manystateroadauthorities,providingsaferandmore
efficientconstructionofbridgesuperstructures.
•ThequalityoftheformClass2finishontheundersideofthe
AustralDeckfloorcaneliminatetheneedforafalseceiling,
maximisingfloortofloorheight.
A flexible and adaptable formwork replacement
•AustralDeckimposesminimumrestrictionsondesigners
andbuilders.Custommadesizesandshapescanbe
manufacturedtosuitconstructionlayoutanddesign
specifications.
• Austral Deck panels can cover the entire width of a
structure, including the cantilever beyond the external
support.RefertoSection8,TypicalInstallationDetails.
•Thesolutionintegrateswellwithconcreteorsteelframed
structures. – Figure 2.
•Cast-initemssuchasferrules,conduitsandotherservice
fixingsandpenetrationscanbeaccommodatedduringthe
manufactureofAustralDeck.
•BalconiesandedgeformscanbecastwithintheAustral
Deckpanel.Thesecaneliminateedgeformworkandscaffold
costs.Integratededgeformsallowsforearlyinstallationof
temporaryorpermanentbalustrades.
•Safetyrailpostholescanbeprefittedtothepanelspriorto
installation,improvingsitesafety.
Economic and fast to install
Austral Deck offers all the advantages of a precast concrete
system;
•Reductioninformworkandproppingcomparedto
conventionalformwork.
•Tofurtherincreaseefficiencyonsite,AustralDeckpanels
maybeproducedwithvoidformerblocksattachedtothetop
oftheprecast.Theseformersreducethevolumeofin-situ
concretetoppingvolumesandreducetheoverallmassofthe
floorstructurebyupto30%.
•Constructiontradescancommenceworkingonthestructure
immediatelyafterinstallation.Serviceductsandconduits
canbeinstalledandaccommodatedintothecastin-situ
portion of the slab.
• Austral Deck can be lifted straight into position, reducing
conventionalinstallationtime.Anaverageof10AustralDeck
panels(coveringanareaof150m2)cantypicallybeinstalled
per hour.
• The panels have a relatively thin layer of concrete, which
makesitlightertotransportandinstall.
•AustralDeckhasthepropertiestoachievefireresistanceand
energyefficiencyprovisionsasspecifiedinrelvantstandards
and building code of practice. Refer to Section 7 in this guide
"FireandThermalResistance".
1.3 ApplicationsAustralDeckhasbeendesignedtobeasflexibleaspossible,
and therefore ideally suited for a broad range of construction
applications.
SomeoftheapplicationsthatAustralDeckissuitedforareas
follows:
•Multi-LevelResidentialDevelopments,including:
>Exposedflatsoffitswithqualityconcretefinish
>Upstandsandbalconiespreformedand/orprecast
>Irregularcolumngrids
> Flexibility of loads, penetrations, ducts and set-downs
•CommercialDevelopments,including:
>Longspanfloorplates
> Flat slabs, reduce losses in ceiling space for tenant
servicesandmechanicalservicesreticulation
>Highloadedareassuchascompactusandstorage
zones
> Good interaction and connection with precast concrete
lift and stair cores, shear walls and other features
>Cast-infittingsforcurtainwallingsystems
• Parking and open-deck applications
>Fastconstructiontimesallowopeningofcarparks
sooner,minimisinglossofcarbaysandmaximising
economicbenefits
>Lightweightconcretespansallowformoreefficient
structures
>Ramps,aislesandtrafficmovementareascaneasilybe
accommodatedwithintheAustralDeckdesign
•Decksandplatforms
>Trafficandpedestrianbridges
>Curvedonandofframpstructures
>Railplatforms
>Marinejettiesandplatforms
• Roofs and lids
> Tunnel and shaft roof panels
> Culverts
> Tank lids
Figure 2 – Integration with steel framed structure.
AUSTRAL PRECAST
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Austral Deck TECHNICAL GUIDE
ThischapterwilldetailthestructuralandgeometricpropertiesofAustralDeck.
AustralDeckhasbeendesignedtobecompletelyflexiblewithregardstodepths,sizesandlayouts.Thestandarddesignsbelow
allowforastreamlineddetailingprocess,asmanyoftheforms,trusses,chairsandjigsarealreadyavailableinmanyofAustral
Precast’sfactoriesaroundAustralia.
2.1 Standard Austral Deck Design Thicknesses, Span Table and Graph
Table 1 shows various standard thicknesses of Austral Deck.
Thereareseveralkeyassumptionsinherentinthestandard
design table, which are detailed as follows.
•Generally,thepanelsareoptimisedtoallowfor60mmor
90mmprecastbiscuitatthebaseandminimum60mmcover
tothetopofthepolystyrenevoidformer.
• Weight reduction and equivalent stiffness factors are based
onatypicalplank,2500x7800mm,with18voidformersof
size550x1000each.
• * Theoretical weight reduction ignores any additional void
formersremovedaroundcolumnsandwalls,penetrations,
cast-inanchors,transferbeamsorotherfeaturesthat
require full thickness concrete.
• Stiffness equivalents are based on elastic section analysis of
theconcretecrosssectiononly.Crackedortransformed
section analysis should be carefully undertaken by the
design engineer.
2. PROPERTIES OF AUSTRAL DECK
mm mm mm mm mm % mm % mm %
AD150 150 60 90 N/A 150 0.0% 150 100% 150 100%
AD175 175 60 115 N/A 175 0.0% 175 100% 175 100%
AD200 200 60 140 50 175 12.7% 199 98% 198 98%
AD225 225 60 165 100 174 22.6% 221 94% 220 93%
AD250 250 60 190 120 189 24.4% 244 93% 243 91%
AD275 275 60 215 145 201 26.8% 266 90% 264 89%
AD300 300 90 210 130 234 22.0% 294 95% 293 94%
AD350 350 90 260 160 269 23.2% 342 94% 341 93%
AD400 400 90 310 210 293 26.7% 387 90% 384 89%
Total Precast Topping Void Theoretical Equivalent Stiffness Equivalent Stiffness Code Depth Panel WeightReduction*(StrongAxis)(WeakAxis)
Table 1 – Standard Austral Deck Design Thicknesses
Table 2 – Span to Depth ratios for residential application
Chart 1 – Span chart guide
Code Total Depth mm
Precast Panel mm
Topping mm
Void Depth mm
UpperSpanLimit Single Continuous mmmm
AD150 150 60 90 N/A 3500 4500
AD175 175 60 115 N/A 4000 5200
AD200 200 60 140 50 4500 6000
AD225 225 60 165 100 5000 6500
AD250 250 60 190 120 5500 7300
AD275 275 60 215 145 6000 7750
AD300 300 90 210 130 6700 8500
AD350 350 90 260 160 7750 10200
AD400 400 90 310 210 8750 11500
Table 2 shows span to depth ratios for residential application of Austral Deck.
Astandard250mmthickslabhasa23%weightsavingofthestructure, withonly7.5%lossofstiffness
AUSTRAL PRECAST
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Austral Deck TECHNICAL GUIDE
Atypicallayoutofplanksaroundasquarecolumnisshown
below in Figure 4.
Thefigureshowsa600x600squareconcretecolumn,withthe
precastplanksstoppingshortofthecolumnby20mmall
round.
Thereisminimum500mmclearancetothecolumninone
direction,and675mmintheorthogonaldirection.Note,
675mmallowsthevoidstoremaininlineandwouldnot
interferewiththereinforcementorrebartrusslayout.
To calculate the effective or average self-weight for this
example,anaverageshouldbetakenoverseveralcolumn
grids.
Note:thepositioningofthe500mmclearancearound
columnsandotherloadbearingelementsisconsideredthe
minimumtoallowforgeneraldetailingofthecolumn-slab
joint.Itdoesnotconsideranypunchingshearperimeter,
whichmayrequirealargersolidregionaroundthecolumn
than depicted in Figure 4. Refer to Section 4.7 for further
details on Punching Shear.
AnexamplecalculationisshownoppositeinSection2.2.3.
2.2.3. Multi-Span Weight Calculation Example
The basic self-weight calculations take into account the
generalproposedlayoutfora2.5mx7.8mplank,including
200mmsolidsectionslongitudinallyand400mmsolidplank
ends.
TheexampleshowninFigure5showsaslabof2x2gridbays
of7.5mx7.8meach.
The250mmslabhas9columnseachof600x600.
Usingatypicalcasewheretheslabbeneathacolumnis
includedintheslabvolumesthetotalvolumeofthisslabis:
15 × 15.6 × 0.25 = 58.5m3
Excludingthevoidfreeareasaroundthecolumnsthenormal
reductionof24.4%equatestoatotalvolumeof44.2m3.
Howeverthereareanumberofsmaller600x550voidsaround
thecolumns.Thetotalvoidvolume:
[16 × 0.4 × 0.55 + ( 12 × 18–16) × 1 × 0.55] × 0.12 = 13.62m2
Volume Reduction = 13.62 = 23.2%
58.5
Iftheslabweretohavesetdowns,wallsandfolds,asislikely
foraresidentialapartmentcomplex,thevolumereduction
maywellreduceto20%orbeyond.
2.2.4. Calculations Using Software
Itispossibletouse3Dmodellingsoftwaretocalculaterough
slabvolumesandthereforeself-weights,includingTekla,
Autodesk Revit or Bentley Microstation.
Whenusinganymodellingsoftware,thedesignerand
draftspersonshouldalwayshaveinmindtheadditional
complexityofmodellingvoids,andtakecarenottouseany
volumeoutputswithouthandcheckingtheresults.
Figure 4 – Plan of Austral Deck Around Column
2.2 Calculation of Austral Deck Weight Reduction
The accurate calculation of the weight reduction is critical to
the design of the structure.
Structuralself-weightmustbeincludedforallcalculationson
slabperformance.Iftheself-weightreductionduetothevoid
formersisignoredthentheslabwillbecomeneedlessly
conservative both for strength and serviceability calculations.
Asadesigner,onemustalsorememberthatforanyconcrete
spanningelement,serviceability(i.e.stiffness)effectsare
multipliedandamplifiedwiththeadditionaleffectsofcreep
andshrinkage.Insomecases,thiscancausesignificantover
orunder-estimationoverthelongtermlifeoftheproject.
Self-weighthasflow-oneffectstotheverticalandlateral
supportingelementsofthestructure.WhilsttheAustralDeck
designernormallywouldonlyconcernthemselveswiththe
designofthesuspendedslabs,anymaterialchangetothe
self-weightoftheslabswillhaveflow-oneffects,byincreasing
(ordecreasing)thecolumns,foundationsandtransferbeams
providing vertical support and cores and shear-walls
providing lateral support.
Generally,over-estimatingtheself-weightofthestructure
would provide a conservative design, however for lateral
elements,particularlyfortallandslenderbuildings,the
designershouldalsobecarefulasunder-estimationofthe
building weight would put excessive tensile loads on the lateral
supportsystems,bynotprovidingenoughtie-downforceto
counteract overturning effects.
Lastly,andpossiblymostimportantly,ifAustralDeckis
adoptedonaprojectafterthepreliminaryandconceptdesigns
have already taken place, the designer should be careful not to
increasetheweightoftheslabs,causingaflow-onincreasein
thecostsofalltheverticalandlateralelementsabove.
2.2.1 Basic Self-Weight Calculations
Calculate self-weight based on an average slab thickness and
average reduction due to the voids.
Forexample,takingatypical2.5mx7.8mplankina250mm
thickconcreteslab,theconcretevolumeis:
2.5×7.8×0.25=4.875m3
Overtheplankarea,thereare18voids,in6rowsx3columns.
Each void is:
550mmx1000mmx120mm,or0.066m3 per void.
Intotaltheconcretevolumefortheplankistherefore:
2.5×7.8×0.25–18x(0.55×1×0.12)=3.687m3
The total average reduction in the concrete slab is:
1 – 3.687
=24.4%
4.875
Fromastartingpointofa250mmslab,thisistheweight
equivalentofa189mmslab.
2.2.2. Refinements to the Self-Weight
The basic self-weight calculations take into account the
generalproposedlayoutfora2.5mx7.8mplank,including
200mmsolidsectionslongitudinallyand400mmsolidplank
ends.
However,therearemanymoreareaswhereitmaynotbe
possibletoachievethemaximumandmostefficientvoid
arrangement.
Itisadvisedthatthereisaminimumof500mmclearance
aroundallloadbearingelementsandconnectionsonatypical
slab.Thatincludesloadbearingcolumns,wallsandcores,as
wellastransfers,steps,foldsandbathroomsetdowns.
Insomecases,itmaynotbefeasibleorpracticaltousevoid
formersatall,usuallyoncetheslabdepthnarrowstounder
175mm.
TypicalAustralDeckdimensionsandcrosssectionsareshowninFigure3.
Figure 3 – Austral Deck Cross Sections
AUSTRAL PRECAST
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Austral Deck TECHNICAL GUIDE
2.3 Calculation of Austral Deck StiffnessThe elastic stiffness of a suspended slab (or any structural
element)issolelydependentontwoproperties;
•Materialproperties,E,theYoung’sModulus
•Geometricproperties,I,theSecondMomentofInertia
Theeffective,transformedstiffnessofasuspendedslab
dependsonanumberofnon-linearandbehavioural
propertiesoftheconcretematerialandlayoutwithinthe
structure,including;
•Extentofcracking,influencedbyreinforcementratio,
concretematerialandhorizontalprestressasperAS3600
sections8.5.3and9.3
•Loadduration(ψfactors)andDeadtoLiveLoadratios
•Creep,influencedbyenvironmentalconditions,concrete
strength and hypothetical slab thickness as per AS3600
section3.1.8
•Shrinkage,influencedbyenvironmentalconditions,
concrete strength and hypothetical slab thickness as per
AS3600 section 3.1.7
Generally in the case of Austral Deck slabs, the calculation of
stiffness is no different, however the designer should also take
the precast concrete panel joints into consideration. For
example,stiffnessacrosspaneljointsevery2.5mona10m
spanmaywellbereducedby10%,asindicatedinsection
2.3.3.
Ingeneral,weignoreanychangestotheYoung’sModulusof
the section, as the concrete is usually a relatively standard
strengthmix,withwell-knownproperties.Concrete
specificationisdiscussedfurtherinthisdocument.
Thegeometricstiffnessdependsonthelayoutandpositionof
thevoidformsandforfullytransformedsections,thelocation
ofthereinforcement.
Forcomputermodellingpurposes,thevoidsareconsidered
usingatraditionalelasticmoduluscalculation.
FortheexampleinSection2.2.3thestiffnessofaplankis
calculated below:
2.3.1. Calculation of the Neutral Axis – Elastic Section
The neutral axis of the cross section is found as follows:
Q = ∑y∙dA
= (2.5 × 0.25m) × 0.125 – 3 × (0.55 × 0.12) ×0.120)
(2.5 × 0.25m) – 3 × (0.55 × 0.12)
= 127.3mm
2.3.2. Calculation of the Moment of Inertia
TheMomentofInertiaofthecrosssectionisfoundusingthe
parallelaxistheoremasfollows,assuminganelastic,
uncracked section.
Ixx = ∑y2∙dA
= bd3 12
+ Ay2 (Concrete minus voids)
= 2.5 × 0.253 0.55 × 0.123 12
+ 2.5 × 0.25 (0.125-0.1273)2 – 3 12
– 3 (0.55 × 0.12) (0.12 - 0.1273)2
= 3010 × 106 mm4
Withoutvoidformers,theMomentofInertiaoftheequivalent
section would be:
Ixx = 2.5 × 0.253
= 3255 × 106 mm4
12
The reduced stiffness in this case is only:
3010 3255
= 92.47%
Inotherwords,forastandard250mmthickslab,thereisa
23-24%weightsavingofthestructure,withonly7.5%lossof
stiffness.
( )
Figure 5 – Typical Multiple Span Austral Deck LayoutNote: Refer to 2.1 about Theoretical Weight Reduction. Some voids might be required to be removed to place the splice bars.
AUSTRAL PRECAST
/ 16 / / 17 /
Austral Deck TECHNICAL GUIDE
3.1 Design PrinciplesThischapterprimarilydiscussestheuseofcomputer
modellingsoftwaretoanalyseanddesignAustralDeckina
varietyofprojectsettings.Thechaptermostlyusesexamples
andspecificsettingsfromRAMConcept,byBentleySystems,
however the general principles can be applied to any internally
recognised software package, including SAFE/ETabs (by
ComputersandStructuresInc),RAPT(byPCDC),Slabs(by
Inducta),Strand7,SAP2000,DIANAandotherFiniteElement
Analysis packages.
Ingeneral,thedesignoftheAustralDeckconsistsoftwo
design stages
1st Stage : Design as formwork
Must be designed for
•Liftingduringmanufacturing
• Transport
•Liftingduringinstallation
•Constructionloadsduringuseasformwork
2nd Stage: Final in-use slab design
• Must be designed for strength and serviceability for
in-servicesituationasperconventionalreinforcement
concrete suspended slab
3.2 General ModellingThe concept and general properties of Austral Deck can be
analysedanddesignedusingregularmethods,conceptsand
codesthatwouldnormallybeemployedtodesignareinforced
concrete suspended slab.
Ingeneral,thedesignerneedstotakeaccountofthefollowing
properties and changes:
•Structuralmass–changingtheconcretematerialproperties
toaccountforvoidformers.
• Structural stiffness – changing the slab shape properties to
accountforvoidformers.
• One vs Two-way spanning – changing the shape properties
to account for non-isotropic properties of the precast joints
andvoidformershapes.
3.2.1. Outputs from Modelling
Just like an ordinary suspended concrete slab, Austral Deck
canbemodelledusing1-D(striprun),2-D(areaplan)or3-D
(fullbuilding)software.
Thedesignercanusethenormalsoftwareoutputssuchasload
run-downs,bendingmomentsanddeflectionstodesignand
design-check the suspended slab.
Somesoftwarehasalsobeenspecificallydevelopedtooutput
detaileddesigns,includingstrip-runanalysis,reinforcement
design and detailing and even bar bending schedules. Any
outputrelatedtothereinforcementandstripanalysisof
AustralDeckshouldbecarefullychecked,assomeofthe
detailingrequirementsaredifferenttoanormalsuspended
reinforced concrete slab.
3.2.2. Code Compliance
AustralDeckhasbeendesignedsuchthatitiscodecompliant
with all of the standard design and construction codes that
exist around the world. These include:
• AS3600-2009 – Concrete Structures
•AS3610-1-2010–FormWorkforConcrete
• Eurocode 2 – 1992-1-1 - Design of Concrete Structures
(Europe)
•BS8110–StructuralUseofConcrete(UnitedKingdom,now
supersededbyEurocode2)
•ACI318-BuildingCodeRequirementsforStructural
Concrete(NthAmerica)
•NZS-3101–ConcreteStructuresStandard(NewZealand)
Thedesignershouldmakethemselvesfamiliarwiththe
particularcoderequirementsforanalysis,designand
detailingfortheregionthatismostrelevanttotheproject.
Inaddition,thedesignershouldalsomakethemselves
familiarwithadditionalcoderequirementsformaterialsand
testingofreinforcement,concrete,formwork,temporary
works and propping that is relevant to the project location.
3.3 Using Ram ConceptRAMConcept(byBentleySystems)isatwo-wayanalysis
package,usingFiniteElementAnalysis(FEA)todetermine
loadsandactionsforasuspendedconcreteslab.Itcanbe
customisedandcanbeusedtodesign,checkanddetail
concrete slabs, including Austral Deck slabs.
3. MODELLING AUSTRAL DECK
Figure 6 – Elastic Analysis of Panel Joints
2.3.3. Calculation of Elastic Stiffness Allowing for Joints
The calculation of a reduction of stiffness based on the precast
concretejointscanbeestimatedbasedonsimplelinearelastic
calculations,butadetailedfiniteelementmodelmaybemore
useful.
Forexample,Figure6belowaretwospans,approximatinga
280mmthick,1000mmwideconcreteslabspanning10m.The
lowerspanhasthreejointsat2500mmcentres,wheretheslab
thicknessisreducedby60mm.
Thejointsaresettobe20mmwideandtheslabinthejointis
raisedsuchthatthetopofslabremainsconstant(i.e.elastic
neutralaxisisraisedby30mm).
Thedeflectionforthemodelbelowhasincreasedbybetween
1%and2%overallatthemidspan.
Itshouldbenotedthatthebelowcaseisforasolid,elastic
section only, and does not include effects for voids,
transformedsections,creep,shrinkageetc.Onlytheimpactof
thepaneljointsaremodelled.
Whilstthejointlocationmayseemtrivial,theoverimpacton
deflectionmaybecritical,andthelocationofjointsshouldbe
positionedwherepossibletoproduceminimalimpactonthe
slab, such as the one-quarter to one-third points of the slab
whereapointofinflectionexists.
0.000 -0.1030.000 -0.1110.000 -0.1030.000 -0.0790.000 -0.043 0.000 -0.079
0.000 -0.043
0.000 -0.1020.000 -0.1100.000 -0.1020.000 -0.0790.000 -0.043 0.000 -0.079
0.000 -0.043
0.000 0.000
0.000 0.000
0.000 0.000
0.000.0.000
AUSTRAL PRECAST
/ 18 / / 19 /
Austral Deck TECHNICAL GUIDE
3.3.2. Average Slab Thickness
Designers should also take care when calculating the average
density for highly variable slabs, such as residential slabs with
bathroomandwet-areasetdowns,balconiesandclosely
spacedloadbearingelements.
Eachoftheseitemswouldaltertheaverageslabthicknessand
density reduction.
The designer should always err on the conservative side of
judgementwhencalculatingaverageweightreductions.For
theexampleshowninFigure23,aresidentialslabmayhavea
reductionof10-12%,withanequivalentdensityof2112–
2160kg/m3.
Forlargefloorareas,itisalsopossibletoaddmultipleslab
typeswithmultipledensities,asperTable4.
3.3.3. Reduced Concrete Stiffness
Different software packages have the ability to directly
influenceconcretestiffnesseithergloballyorlocallyincertain
areas of the slab.
Structuralstiffnessisproportionaltobothmaterial(Young’s
ModulusE)andgeometricstiffness(MomentofInertiaI).
Thematerialstiffnessvalueswereunmodifiedinthematerial
settingsabove,astheconcretematerialisnotactually
changing when using Austral Deck.
RAMConceptcanmodifygeometricstiffnessbyalteringthe
slabthicknessordirectlywithmodificationcoefficients.
Itisthedesigner’sprerogativeastowhichoptionismodified,
butoneshouldalwaysremembertheflow-oneffectsofeach
option. For instance, reducing the slab thickness in RAM
Concept would directly reduce the structural self-weight, and
dramaticallyreducethecapacitycalculationsforBending
Moment,BeamShearandPunchingShear.
Itisrecommendedtoreduceonlythebendingstiffness
coefficientsasperFigure8.ForRAMConcept,thecoefficients
arefoundintheSlabPropertiesoftheMeshInputwindow.
Table 4 – Reduced Austral Deck densities for regular and bathroom slab areas
Figure 8 – Slab properties showing Austral Deck concrete mix and custom reduced stiffness
MIX NAME Density (kg/m3)
Density For Loads(kg/m3)
f 'ci (N/mm2)
f 'c (N/mm2)
25 MPa 2400 Density 15 20
32 MPa 2400 Density 20 25
40 MPa 2400 Density 20 32
40 MPa 2400 Density 20 40
50 MPa 2400 Density 20 50
65 MPa 2400 Density 20 65
40 MPa Austral Deck Bathroom Setdown 2400 Density 20 32
RAMConceptcanundertakeanalysesandcodecompliant
detailingforavarietyofcountryspecificconcretestandards.
OnlyrelativelyminoradjustmentsarerequiredtoenableRAM
ConcepttobecompatiblewithAustralDeck,whichare
detailedbelow.Itisimportanttonote,howeverthatthereare
manyotheroptionsinRAMConceptthattheAustralDeck
designer can be used to adjust or “tweak” the analysis or
design.Designersshouldalwaysfamiliarisethemselveswith
thelimitationsofthesoftwareandundertakesensitivity/
varianceanalysisrunstoascertainthemagnitudeofimpact
on any of these options.
Note:Thefollowingexamplesarebasedoncurrentmenusand
screenshotsfromRAMConceptCONNECTEdition,
v6.00.01.006x64.Otherversionsmayhaveslightlydifferent
menuconfigurations.
3.3.1. Adjustment for Structural Weight
Oncreatinganew“ElevatedSlab”model,thedesignershould
selectthe“Materials”screenfromthenavigationmenu,
Figure 7:
FromtheMaterialsscreen,thedesignershouldselecta
concretestrengthmostlikelytobeused–generallythiswould
be32MPaor40MPa(N32orN40)gradeconcrete.
Select“AddConcreteMix”andnameittoappropriatelyreflect
theAustralDeckmix,e.g.:“50MPa(AustralDeck).
Copytheconcretemixproperties,ensuringthatthestrength
andstiffnesspropertiesremainthesameastheordinary
concretemix(refertoTable3).
ReducetheconcreteDensitybyafactorcalculated/estimated
tobetheslabaverage,allowingforweightreductionsfrom
voidformers.
Forexample,forarectangular,regularcarparkslabin
Figure4themaximumdensitymightbe24.4%,butthe
averagereductionmightbe20%.Conservatively,thedesigner
mayevenuse17%asaninitialassumption.
For this case, the density would be:
2400kg/m3×(1-0.17)=1992kg/m3
Note:thedesigndensityofnormalconcreteisspecifiedby
AS3600-2009,Section3.1.3as2400kg/m3.Inpractice,the
actual density of concrete changes with the concrete and
aggregatespecifications,quantityofreinforcementandother
properties.
The designer should also take care to check if the density
properties are used in calculation for any other structural
propertiesthatmightimpacttheresultsoftheanalysis.
InthecaseofRAMConcept,itispossibletospecifyaseparate
DensitypropertyfromDensityForLoadscalculation.Itis
highlyrecommendedthatthedesignerruntheanalysisfor
both options and check if any differences in the results are
significanttothecalculations.
Itisalsoimportantthattheconcretestrengthandstiffness
characteristics,suchasf’ci,f’
c, E
ci and E
cremainthesameas
thetraditionalconcretemix–thesewillbealteredlater.
Figure 7 – RAM Concept Menu
Table 3 – RAM Concept Concrete Mix Properties
MIX NAME Density (kg/m3)
DensityForLoads (kg/m3)
f 'ci (N/mm2)
f 'c (N/mm2)
f 'cui (N/mm2)
f 'cu (N/mm2)
Poisson's Ratio Ec Calc User Eci
(N/mm2)User Ec (N/mm2)
20 MPa 2400 Density 15 20 18.75 25 0.2 Code 21000 25000
25 MPa 2400 Density 20 25 25 30 0.2 Code 25000 27000
32 MPa 2400 Density 20 32 25 40 0.2 Code 25000 31000
40 MPa 2400 Density 20 40 25 50 0.2 Code 25000 34000
50 MPa 2400 Density 20 50 25 60 0.2 Code 25000 38000
65 MPa 2400 Density 20 65 25 80 0.2 Code 25000 43000
32 MPa (Austral Deck) 2400 Density 20 32 25 40 0.2 Code 25000 31000
AUSTRAL PRECAST
/ 20 / / 21 /
Austral Deck TECHNICAL GUIDE
3.3.7. Austral Deck and RAM Concept Design Strips
RAM Concept uses Design Strips to integrate design actions
suchasbendingmoments,shearsandsupportreactionsand
createaone-dimensionalspan.Thedesignorspanisthen
split into several regular cross sections which are analysed.
Reinforcementquantities(inmm2)aredeterminedforthe
design load envelopes over the design cross section. Finally,
the software takes all the design sections along a particular
spanandappliescodecompliantdetailingrulestolayoutthe
reinforcement.
3.3.8. RAM Concept and AS3600-2009 Implementation
The designer should be aware of the various inclusions and
exclusions that RAM Concept applies and ensure that
adequatehand-checksareperformedtomakesurethereisno
areasoftheslabthatareexcludedfromtherun.
For instance, RAM Concept does not apply all the various
requirementsfromAS3600-2009,orappliesitsown
interpretationsofsomeofthevariousdesignrequirements.
ThisisdetailedintheRAMConceptmanual.
SomeofthedesignlimitationsthatRAMConceptappliesare
pertinent to Austral Deck designs, as follows:
Initial Service Load Case
RAM Concept does not take into account the differential age
between the precast plank and topping portion of Austral
Deck.
Concrete modulus
RAMConceptusestheformulaforEcandEciasspecifiedby
the equations in AS3600-2009 Section 3.1.2, not the values
specifiedbyTable3.1.2.
f 'cmvaluesusedintheequations,however,aretakenfrom
Table 3.1.2. in AS3600.
Low Ductility Rebar
RAMConceptdoesnotapplythelowductility(ClassL)rules
thatwereupdatedaspartofAmendment#2ofAS3600-2009.
Thisisparticularlyrelevantforthemeshreinforcementplaced
within the precast section of Austral Deck.
Minimum Reinforcement
RAMConceptusesAS3600-2009Section8.1.6andSection
9.4.3.2forminimumreinforcementinspandirections.
Section9.1.1isimplementedviaSection8.1.6.1forspanning
reinforcement.Thismayresultindifferentreinforcement
quantities in Austral Deck planks.
Crack Control
AS3600-2009Section9.4.1(c)and(d)areignoredwhenthe
slabenvironmentisspecifiedas“protected”,whichisthe
typicalsettingforinternalslabs.Thismaybeunconservative
forAustralDeckslabsandshouldbecheckedmanually.
Axial Forces
Axialforcesaresometimestakenintoaccount,dependingon
thedesignstripsettings,howeverfor“T”,“L”,or“Z”beams,
Austral Deck designers should take care that the design strips/
sectionsincludetheentirebeamflangearea,otherwise
significantout-of-balanceaxialforceswillbeappliedintothe
plankzonesoftheAustralDeckslab.
Reinforcement depth
Austral Deck designers should carefully specify the design
locationandactuallocationoftheLayer2reinforcement,i.e.
thebarsplacedonthebottomofthein-situslab,sitting
directlyonthebottomoftheprecastplank.Insomecases,
thesebarsmaynotbeproperlyincludedasbottomface
reinforcement.
3.3.9. Austral Deck and RAM Concept Deflection Analysis
Accuratepredictionofslabdeflectionscanbeadifficulttask
andisdependentonbothanalysisanddesignparameters
including:
•Loadingandloadhistoryestimatesovershortterm(days)
andlongterm(years)
•Estimationofslabcrackingandeffective/transformedslab
section properties
•Tensionandcompressionreinforcementratios
•Interactionbetweencrackedconcreteslabsand
reinforcement
•Estimationofcreepandshrinkageproperties
•Estimationofshortandlongtermconcretestrengthand
stiffness(asdesigncomparedtoas-constructed)
•Estimationofconcreteratesofstrengthgainover24hours,
30 days and 30 years.
• Slab age at de-propping and loading
RAM Concept provides load history calculations which are
then reconciled to the cracked section analysis in orthogonal
directions.(Figure10).
Figure 10 – RAM Concept load history options
3.3.4. Isotropic vs Orthotropic Stiffness
Whenmodellingasuspendedslabinafiniteelementsoftware
environment,itisoftenpossibletoadjusttheindividual
stiffnesscoefficientsseparately.
InthecaseofRAMConcept,Figure7showsthe6degreesof
slabmovement,asfollows:
•KMr Bendingstiffnessaboutprimarydirection
(aboutRaxis)
•KMs Bendingstiffnessaboutsecondarydirectory
(aboutSaxis)
•KMrs Torsionalstiffness
•KFr In-planeaxial/membranestiffnessinprimary
direction
•KFs In-planeaxial/membranestiffnessinsecondary
direction
•KVrs In-planeshearstiffness
Wherecustomcoefficientsareused,theorientationofthe
R-axis is critical.
For Austral Deck slabs, it is good practice to orientate the
R-axis in the direction of the Austral Deck plank. Whilst
Austral Deck has been designed to be a two-way suspended
slabsystem,theplanks,voidsandjointsinteractsuchthatthe
direction of the deck is considered the stronger and stiffer
direction.
ForRAMConcept,ifallcoefficientsare1,theslabisperfectly
isotropic, or two-way spanning. Whereas, for an idealised
one-way slab, RAM Concept defaults to
KMr=0.001andKMrs=0.5.
3.2.5. Austral Deck and Orthotropic Stiffness
Inanidealdesign,AustralDeckisconsideredtobealmost
isotropic. As Table 1 indicates, the difference between strong
andweakaxisreductionsissubtle.InthecaseofAD250the
differenceis93%comparedto91%.
Inpractice,forlongerAustralDeckspans,plankdimensions
maybe8-9mx2.5m.Thisresultsin3-4timesmoreplank
jointsinthesecondarydirectionthantheprimarydirection.
Forproperly(andideally)laidoutslabplans,thecumulative
impactofthejointsmayreducestiffness(andincrease
deflection)byasmuchas5%overlargerspans.Thisalsohas
theeffectofredistributingprimaryandsecondarydirection
momentswhichwillalterthereinforcementdesignand
placement.
3.3.6. Orthotropic Stiffness and Australia Code Compliance
Itisimperativethatanyvariationtotheslabstiffnesstakes
into account both the actual, real-world differences in the
structuralpropertiesoftheslab,butalsothelimitations
imposedbyanyrelevantdesigncodesandstandards.
For instance, Australian Standards AS3600-2009 describes
methodsforstructuralanalysisinSection6.Inparticular,
Section6.9describestheuseofIdealisedFrames,whereby
positiveandnegativemomentsinbothprimaryandsecondary
axesareapportionedtocolumnandmiddlestrips.
RAM Concept enables the designer to split the suspended
slabintovariousdesignstrips.Ifdesignstripsaresetup
automatically,RAMConceptwilldefaulttousing“CodeSlab”
layout rules, which generally apportion the strips in
accordance with AS3600, Section 6.1.
ForAustralDeckdesigns,theuseofprimaryandsecondary
stiffnessmodifierswillsignificantlyinfluencethe
apportionmentofloadandthereforebendingmomentintothe
columnandmiddlestrips.
Thedesignershouldtakecaretoensurethatthemoment
redistributiondoesnotexceedthelimitsofredistributionthat
is allowed by the code. For instance, AS3600-2009 Table
6.9.5.3limitsthemomentdistributionasfollowsinTable5:
Table 5 – Design strip distribution from AS3600-2009 Table 6.9.5.3
Figure 9 – Design column and interior strips as defined by AS3600-2009 Section 6.1.
AS 3600—2009 78
© Standards Australia www.standards.org.au
FIGURE 6.1.4(A) WIDTHS OF STRIPS FOR TWO-WAY SLAB SYSTEMS
FIGURE 6.1.4(B) SPAN SUPPORT AND SPAN LENGTHS FOR FLAT SLABS
Acce
ssed
by
R O
BIR
D A
ND
ASS
OC
IATE
S PT
Y LT
D o
n 21
Dec
200
9
Distribution of Bending Moments to the Column Strip
Bending Moment Under Consideration
Strength Limit State
Servicability Limit State
Negativemomentinaninteriorsupport 0.60 to 1.00 0.75
Negativemomentinanexteriorsupportwithspandrelbeam 0.75 to 1.00 0.75
Negativemomentinanexteriorsupportwithoutspandrelbeam 0.75 to 1.00 1.0
Negativemomentinaninteriorsupport 0.50 to 0.70 0.6
AUSTRAL PRECAST
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Austral Deck TECHNICAL GUIDE
3.4 Austral Deck Design Strip Layout in RAM Concept
Thissectiondiscussessomeofthemodellingoptionsavailable
to Austral Deck designers using RAM Concept.
The layouts are only suggested for various designs, and could
easilybereconfiguredtosuittheAustralDeckdesigner’sown
preferences.
Theexampledesignusedinthissectionhasbeenchosento
demonstratesomedesignstriplayoutoptions,anddoesnot
representareal-worldmodel.
ToensuretheterminologyofRAMConceptremains
consistent,wewillrefertotheslabaxesasLatitude,running
horizontallytothepage,andLongitude,runningverticallyto
the page.
Theslabcontains3spansof8m,6.5mand8mrespectivelyin
theLatitudedirection,and2spansof6.5mintheLongitude
direction.(Figre11–12)
Theoverallflooris250mmthickAustralDeck,with40mm
bathroomset-downs.Thereare200mmwide,1000mmdeep
upstandbeamsontwosidesofthemodel.
3.4.1. Example Design
Figure 11 – RAM Concept strip layout example
Figure 12 – RAM Concept strip layout - 3D render
ItisimportantforthedesignerofAustralDecktotakeinto
accountsomeparticulardeflectioncharacteristicswhichmay
influencethedeflectioncalculation,asfollows:
•TheRAMConceptcreepandshrinkagemodelsarederived
fromACIreport209R-92.Thereissignificantliterature
onlineforthisdeflectionmodel,howeveritisimportantto
notethattheACImodelassumestheinitialloadingtimeis7
days,whereasAS3600assumesinitialloadingis28days.
DesignersshouldeitherusetheACImodelandspecifythe
actualtimeofloading,orusetheAS3600-2009finalcreep
factorsfromTable3.1.8.3,andthenmultiplyby1.326,which
is(k3-7days/k3-28days).
• Designers should also note that the creep factor includes
elastic strain + creep strain.
•ShrinkageRestraintplaysanimportantroleindeflection.
OnlineguidancefromRAMConceptisasfollows:
>0%-unrestrainedorverylightlyrestrainedslabs
(flexiblecolumnsonly,singlestiffelement)
>10%-normallyrestrainedslabs(morethanonestiff
element,someflexibility)
>20%-completelyrestrainedslabs(basementwalls
aroundentireperimeter,etc.causingahighdegreeof
restraint)
• Generally, shrinkage restraint for Austral Deck should be set
between10and15%dependingonthelevelofconservatism
requiredfordeflectioncalculations.
• Whilst designers usually ignore the live load reduction
factorssettingsinRAMConcept,itisimportanttosetlive
loads to their correct load case (Reducible, Unreducible,
Storage,Parking,Roof).RAMConceptusesthesecasesto
determineshortandlongtermcombinationfactorsin
accordance with AS1170.0 Table 4.1. These are then used for
theloadhistory.Forexample,settingresidentialloadingto
“unreducible”wouldapplyψL=0.6andψS=1,ratherthan
ψL=0.4andψS=0.7.Thiswouldobviouslyincreasethe
deflectionoverthelongterm.
•RAMConceptdefaultstousing5000days(132/3years)for
longtermdeflection,butAS3600conventionssuggest30
years, or 10950 days.
Table6isasetofloadhistorysettingsthatmightbetypicalof
aresidentialslab(average250mmthick,32MPa,coastal
environment).
Variationinthesesettings,combinedwithanabundanceof
localisedenvironmentaleffectswillgiverisetodifferencesin
real-worldexperiencesofdeflection.Itishighlyrecommended
that conservative values are chosen, and that the designer
undertake sensitivity analyses with different values to check
thattheslabdesignissufficientlyconservative.
3.3.10. Example – Austral Deck Load History Settings
Table 6 – Typical load history settings for a residential Austral Deck slab
Setting Value Comments
Live Load 1.5kPa(reducible) AsperAS1170.1,toensureshortandlongtermfactorsarecorrect
Load History –Sustained 10950 days Equalto30yearsfortotallongterm
Initial Load Application 7 days AsperRAMConceptRecommendations
Shrinkage Restraint 15%Forexample,aresidentialslab,precastconcretepartywallsandasheercore,
but free to shrink on the edges
Creep Factor 3.8DesigncreepfactorfromAS3600-2009using:
F'c + 32, t
h=250,t=10950,k2=1.127,k3=1.463φ*
cc=2.8,Designcreep=1+φ*
cc
Shrinkage Strain 0.000462FromAS3600-2009,usingbasicshrinkageε*ccsd,b=1000µε,
basedonaggregatesupplyfrom"elsewhere'
AUSTRAL PRECAST
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Austral Deck TECHNICAL GUIDE
Figure 14 – Example plank layout #1
Figure 15 – Example plank layout #2
Flatplateslabscanbemodelledasindividualstripsoras
individual Austral Deck planks.
Inthiscasethe250mmAustralDeckslabwasmodelledwitha
17%reductionallowanceforvoids,butthebathroomswere
modelledwith11%reduction,using210mmthickslabs,
roughlybasedonthereductionfactorsfromTable1.
Figure13presentsareasonablemeshforAustralDeck,
however does not provide a very cost effective plank layout, as
seeninFigure14.ThereareeightprimaryAustralDeck
planksand18secondaryplanks,whicharequiteshort.
Figure15removesoneoftheprimaryplanksandextendsthe
secondaryplanks,reducingthetotalplankcountto18,saving
eight planks in total.
TheAustralDeckdesignermustconsiderthatextraplanks
requireextrapropping,transportandliftingrequirements,
andincreasethenumberofjointsvisibleinthesoffitofthe
slab.
RAMConceptprioritynumberswereused(higherpriority
numbersaremeshedinpreferencetolowernumbers),as
follows:
•Upstandbeams,fulldensity,priority5,meshedasslab
elements
•Bathroomareas,latitudeorientation,priority3
•Generalprimaryspans,longitudeorientation,priority2
• General secondary spans, latitude orientation, priority 1.
3.4.2. Flat Plate
Figure 13 – Example model showing mesh area layouts
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Austral Deck TECHNICAL GUIDE
SomeoftheothercharacteristicsofthestripsinFigures16
and 17 are:
•Alllatitudestripshavetheirreinforcementcoverssetto
minimum–i.e.thedesignedreinforcementallowsfor
bottombarstobelocatedintheplank.Thedesignershould
note, however, that the planks in the latitude direction stop
shortbythewidthofthecolumnplanksspanninginthe
longitudedirection.Bottomlayerreinforcementatthispoint
would not be in the critical section, but needs to be checked
nonetheless.Furtherdetailingrulesforthesecircumstances
are shown in Section 4.
•Latitudestripshavebeensettoroughly2.4mwide,
mirroringtheplanklayout,howeverthestripsareshifted
suchthattheyarecentredonthecolumnslines.Thismeans
thattheedgedesigns(span1-1to1-4and7-1to7-4)would
actually be “half-strips”. The designer could either bear this
inmindwhendetailingthereinforcementonstructural
drawings,orcouldadjustthestripboundariesmanuallyto
exactlymirrortheplanklayout.
•LongitudestripsfollowthetraditionalColumnStrip/Middle
StriplayoutasspecifiedbyAS3600.Thesestripswouldbe
stiffer as they are generally shorter spans and as such the
designer should take advantage of AS3600 detailing
guidelines for positioning of rebar within the effect
compressionwidthofthecolumnstrips.Furtherdetailsare
shown in Section 4.
•Longitudestripsfortheupstandplanksaresetas“Inverted
L”beams,howeverthedesignershouldconsiderusing
manualdesignsectionstoensurethetopdimensioniscutoff
to200mmabovetheslabsurfacelevel.ThisenablesAustral
Deck to provide the upstand plank with a short hob and the
remainderoftheupstandasaprecastwallelement.
Figure 17 – Longitudinal sections generated from design strips
Figure 16 – Latitude and longitude design strips
The design strip layouts in Figure 15 follow the plank layouts
at left for latitude and longitude strips. They are all designed
as “slab rectangle” strips, with the exception of the upstand
beams.
AUSTRAL PRECAST
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Austral Deck TECHNICAL GUIDE
The design strips in Figure 20, particularly in the longitudinal
direction are not altered in layout, however designating the
stripsas“beam”adjuststheeffectivestripwidth,in
accordancewithAS3600-2009Section8.8.
Themaximumslabdeflectioninthiscaseis32-35mm,which
isSpan/295fora10mspan.Thisisconsideredreasonableas
farasspan-to-deflectionratios,butgenerallywouldbe
considered5-10mmtoolargeinabsolutedeflectionterms.
Whenproperlyreinforcedanddetailed,theabovedesignproducesadeflectionprofileasfollows:
Theadjustmentalsoremovestheupstandsontheedgesfrom
the concrete section calculations, in favour of the downstand
band. Note that the stiffening effect of the upstands, including
bendingmomentdistributionisstilltakenintoaccount.
Figure 21 – Banded slab deflection profile
Figure 20 – Longitude strip layout for banded slab
Abandedslab(Figure18&19)representsamorespecificuse
ofAustralDeck,mostlikelytobefoundincarparks,
commercialbuildingsortransferfloors.
Thedeeperbandseffectivelyconfiguretheslabintoaseriesof
one-wayspanningbeamsandone-wayspanningslabs.Ifthe
spansbetweenthebeamsaresufficientlylong,AustralDeck
provideanidealdesigntolimitformworkandproppingand
speed up construction cycles.
Thedeeperbands(usuallyintheorderoftwotimestothree
timestheslabdepth)arestillsufficientlywidetoenable
flexuralcapacityintheirtransversedirection,howeverthere
would not usually be any voids present in the bands. The
bands,therefore,arespecifiedwithnormal,ratherthan
reduceddensity,concretematerials.
3.4.3. Banded Slab
6.5
6.5
8 6.5 6.5
RRS
SRR
S
S
RR
S S RRS
S
Figure 18 – Banded slab layout
Figure 19 – Banded slab 3D render (viewed from below)
AUSTRAL PRECAST
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Austral Deck TECHNICAL GUIDE
4.2 Ductility Requirements in Flexural Reinforcement
Ductilityrequirementsareoneofthefundamentalconcernsof
well designed, conservative concrete structures in accordance
withAustralian(andmostinternational)codesandstandards.
The general ductility principle requires structures that have
beenloadedbeyondthepointoffailuretodeflectsignificantly
withoutcollapse,soastoprovidesufficientwarningtotheir
occupants to evacuate.
AS3600-2009specificallyaddressessomeductilityconcerns.
The changes to the code should be carefully considered in all
Austral Deck designs.
AS3600-2009 section 1.1.2 requires:
ReinforcingsteelofDuctilityClassLinaccordancewithAS/
NZS 4671—
(i)maybeusedasmainorsecondaryreinforcementinthe
formofweldedwiremesh,oraswire,barandmeshin
fitments;but
Whilstthereinforcementlayingsequencewillprimarilybe
definedbytheplankspandirection,thesequenceofthetop
reinforcementlayersaresomewhatmoreflexible.
For Austral Deck slabs, layers 1 and 2 are cast into the precast
concrete plank. Splice bars on layer 3, along with any
additionalsecondaryreinforcementisplacedonthesurfaceof
the plank once the Austral Deck has been positioned on site.
ReinforcementisusuallyreferredtoasLayers1through5,
orB1/T1,dependingonthenormalnamingconventionsofthe
Austral Deck designer. These are detailed in Figure 23:
These bars are usually threaded through gaps in the trusses.
Finally, layers 4 and 5, are placed and tied in the top layer in
thesamemannerasatypicalin-situpouredconcreteslab.
(ii)shallnotbeusedinanysituationwherethereinforcement
isrequiredtoundergolargeplasticdeformationunder
strengthlimitstateconditions.
Generally, throughout the code, the use of low ductility
reinforcement,suchasSLandRLgrademeshesisexpressly
forbidden.However,Section6ofAS3600-2009provides
designguidanceastotheuseof“L”gradereinforcement.
Essentially,positivedesignmomentsareincreasedbyupto
10%,(forexamplewL2/16becomeswL2/14),andmoment
redistribution is not allowed.
AustralDeckusesacombinationoflowductility(L)and
normalductility(N)reinforcementfortheprimarypositive
(mid-span)bendingmoments,andnormalductility
reinforcementforthenegativebendingmoments,over
supports.
ItistheAustralDeckdesigner’sresponsibilitytodetermine
theratioofLtoNductility.Onesuggestionistoprovide
sufficientNgradereinforcementtocomplywithultimateloads
under“fire”or“earthquake”loadconditions.Thisistypically
W*=DL+0.3xLLinaccordancewithAS1170.0.
4.3 Reinforcement Laying Sequence
Figure 23 – Reinforcement bar laying sequence
Figure 22 – Cover requirements for Austral Deck planks
Table 7 – Extract from AS3600-2009, Table 4.3 - Concrete Exposure Classification
Table 8 – Extract from AS3600-2009 Table 4.10.3.3 - Concrete Cover
Thefollowingchapterdiscussessomeofthemorespecific
requirementsofAS3600-2009,ConcreteStructures.The
standardhasspecificdesignanddetailingrequirementsthat
alldesignersarerequiredtocheckaspartofthenormal
design process.
Thischapterwilldiscussthoserequirements,andhowthey
impactthedesignofAustralDeckslabs.
4.1 Concrete Cover4.1.1. Code Requirements
ThecoverrequirementsforAustralDeckslabsarethesame
asforanynormalreinforcedconcreteelement,withone
exception.
Minimumcovertothebase(soffit)andsidesoftheAustral
DeckprecastplankcanbetakenfromAS3600-2009,Table8
inthisguide,ratherthanTable4.10.3.2.Thisisjustifiedasthe
Austral Deck planks are cast on rigid steel casting beds,
off-siteinaprecastconcretefactory.Itisassumed(andshould
alwaysbecheckedbythedesignengineer),thattheprecast
factorywillemployrigorousqualitycontrolandchecking
procedures.
Theminimumcoverrequirementsforenvironmental
conditions,asdetailedinAS3600-2009Table4.8.1andTable
4.8.2shouldalwaysbeadheredto,forAustralDeckslabsclose
to or in contact with the ground, especially in aggressive soils.
Carefulreinforcementlayingdirectionsshouldbefollowedfor
thegeneralmesh,especiallywiththestandard60mmAustral
Deck biscuit thickness. These are represented in Figure 22.
The Austral Deck designer should also check the exposure and
durabilityrequirementsfortheAustralDeckplanks,
especiallyforthesoffitsofexternalelementssuchas
balconies.
Table4.3ofAS3600-2009,(Table7)inthisguide,detailsthe
exposureclassificationforvariousconcreteelements.Section
4oftheStandardindicatesthemostcommonelementsthat
would be used for Austral Deck planks.
ReferencingtheabovetablesfromAS3600-2009,AustralDeck
projectsintropicalclimaticzones,oranyAustralDeckplanks
locatedexternallyandwithin50kmofthecoastwouldbe
definedasB1.Theserequireminimum25mmcoverfor40MPa
concreteinaccordancewithAS3600.Note:tropicalzonesare
alsodefinedinAS3600,andgenerallyrefertoareasNorthof
20°S in Western Australia and Northern Territory, North of 23°
in Queensland.
4. AUSTRAL DECK AND AS3600 DETAILING REQUIREMENTS
Surfaces of members in above ground exterior environments in areas that are:
(a)Inland(>50kmfromcoastline)environmentbeing: (i)Non-industrialandaridclimaticzoneA1 (ii)Non-industrialandtemperateclimaticzoneA2 (iii)Non-industrialandtropicalclimaticzoneB1 (iv)IndustrialandanyclimaticzoneB1 (b)Near-coastal(1kmto50kmfromcoastline), anyclimaticzoneB1 (b)CoastalandanyclimaticzoneB2
Required cover where repetitive proceedures and intense compaction or self-compacting concrete are
used in rigid formwork
Exposure classification
Requiredcover,mm
Characteristic strength (f 'c)
20 MPa 25 MPa 32 MPa 40 MPa ≥50 MPa
A1 20 20 20 20 20
A2 (45) 30 20 20 20
B1 – (45) 30 25 20
B2 – – (50) 35 25
C1 – – – (60) 45
C2 – – – – 60
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Austral Deck TECHNICAL GUIDE
The calculation of splice bar quantity and length is required to
becarefullydeterminedforAustralDeckslabs,astraditional
“lappedsplices”arenotusuallyapplicable.(Figure25)
4.7 Punching Shear4.7.1 General Design Issues
Punching shear for Austral Deck slabs needs to be carefully
designedandchecked,especiallywithlarger,flat-platetype
slab designs.
InAustralia,itisgenerallyaccepteddesignpracticetoeither
use AS3600 Section 9.2 or to use the Eurocode EN 1992-1-1
Section 6.4.4
Bothoftheabovedesignmethodshavesignificantbodiesof
researchbehindthem,andarenotcomparedspecificallyinthis
manual.
Ingeneral,AustralianStandardAS3600treatspunchingshear
usingclosedreinforcementtieslaidinatorsionaldesignstrip
acrossthecolumn.Thedetailingrequiresthetiestobeplaced
overaquarter-spanineachdirectiontoadjacentcolumns.
TheEurocode(andtheoldBritishStandard8110)modelsa
series of concentric shear planes or rings progressing outwards
fromthecolumninquestion.Verticalshearreinforcementis
placedinacruciformorradialpatternoutwardsfromthe
columnuntilthepunchingshearperimeterissufficientlarge
enoughtocarrytheload.Thereinforcingisusuallyintheform
of individual hooks or “S” shape rebar, or proprietary studs
tack-welded on to light bars such as Ancon Studrail.
4.7.2 Punching Shear Reinforcement and Austral Deck
ForAustralDeckslabs,itisusuallysimplertousethe
Eurocode to both check and design for punching shear, and
the use of shear studs rather than closed ligatures is certainly
easier for installation.
Where required, the punching shear studs can be installed
into the precast biscuit in the factory to a precisely laid out
position, and generally do not interfere with the trusses or
bottomreinforcing.
Itiscriticallyimportantthatallvoidformersareremoved
fromthepunchingshearperimeter,howeverwidethatmay
be.Thisinturnwillimpactthetotalslabweightandmay
requirerecalculationofrun-downloadstocolumnsand
foundations, all of which should be taken into account by the
Austral Deck designer.
4.7.3 Basic Punching Shear Checks
Prior to undertaking detailed checks and design, it is often
usefultodetermineabasicpunchingshearcapacityaround
thecolumns.ForthispurposeeitherAustralianorEuropean
codes can be used.
The Austral Deck designer should establish the capacity of the
toppingcomponentoftheAustralDeck,excludingtheprecast
biscuit.Thisisconsideredtheabsoluteminimumcapacityasit
ignoresupto60mm(or90mm)oftheconcretedepth.
4.6 Calculation of Splice Bars
Figure 25 – Splice bar calculation of forces
4.4 Detailing of Span Direction Reinforcement
PrimaryreinforcementdetailinginaccordancewithAS3600is
specifiedinsection9.1.3.1forsuspendedslabs.Thisincludes,
amongothers,thefollowingkeyrequirements:
•Requirementforanchorageofpositive(bottom)flexural
reinforcementatendsupports–generallyatleast50%ofthe
totalflexuralreinforcement,anchoredtoatleastthelarger12
bardiametersorD,theslabthickness.
•Requirementofatleast25%ofthepositive(bottom)flexural
reinforcementtoextendpastthenearfaceofaninternal,
continuous support point, typically to full anchorage of 25 bar
diameters.
4.4.1 End Supports
For Austral Deck planks supported by a precast concrete wall,
thefirstrequirementcanbemetbythefollowing:
1. Provide screw-in ferrules, rip-boxes or other proprietary
reinforcementequivalenttoatleast50%oftheflexural
reinforcement.
2.Provideafulllapofferruleswiththebottomreinforcement,
asperAS3600Section13.2,toaminimumlengthofLsy.t.lap
Forplankssupportedbymasonryorbrickwork,thiscanbe
achievedbyprovidingcogsontheprimarybottom
reinforcement,asthecogswillprovide50%anchoringin
accordance with AS3600 Section 13.1.2.6
4.4.2 Internal Supports
Atinternalcolumnsorwalls,atleastonequarteroftheflexural
bottomreinforcementshouldbeextendedpastthefaceofthe
support. This will require additional splice bars to be added to
the Austral Deck once it has been installed on site. Refer to
Section 4.6 in this guide for notes on calculation of splice bars.
Figure 24 below shows a typical splice bar detail at an internal
columnlocation.Notethatonly25%oftheflexuralbarsare
required to be spliced.
4.4.3 Negative Reinforcement
Standarddetailingrulesremainapplicableforthe
conventionallylaid,negativeortoplayersofreinforcement.
One critical such rule is AS3600-2009, Section 9.1.2,
Reinforcementandtendondistributionintwo-wayflatslabs.
Intwo-wayflatslabs,atleast25%ofthetotalofthedesign
negativemomentinacolumn-stripandadjacenthalfmiddle-
stripsshallberesistedbyreinforcementortendonsorboth,
locatedinacross-sectionofslabcentredonthecolumnandof
a width equal to twice the overall depth of the slab or drop
panelplusthewidthofthecolumn
GiventhatthemajorityofAustralDeckslabsaretwo-way,
withgenerallyflatsoffits,theaboverequirementwillmost
likely apply.
4.5 Detailing of Cross Direction Reinforcement
IftheAustralDeckdesignerreducesthestiffnessofatwo-way
slabto50%orless,thenitislikelythatthesecondary
directionreinforcementrequirementwillbealmostentirely
metbythecrossrodsofthemeshcastintotheprecastplank.
Typically,forSL92*mesh,thisis287mm2/m,orthe
equivalentofN12rebarat400mmcentres.
Thedesignerwillneedtobemindfulofductilityrequirements
(refertosection4.2).
Thenumberofsplicebarsrequiredforthecrossdirection
reinforcementwouldthenbecalculatedasaproportionofthe
crossdirectionreinforcement.Forinstance,if180mm2/m
reinforcementisrequiredand287mm2/misprovided,then
splicebarstheequivalentofN12at600mmcentreswouldbe
required,providing183mm2/m.Thisisequivalenttosplicing
everythirdrodfromSL92*(8.55mmbars).
* The common mesh size used for manufacturing Austral Deck is SL72.
Figure 24 – Typical internal support splice bar locations
AUSTRAL PRECAST
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Austral Deck TECHNICAL GUIDE
4.8 Longitudinal ShearInzonesofhightransverseloads,longitudinalshearcan
becomesignificantforanycompositestructure,including
Austral Deck.
InthecaseofAustralDeck,theshearcanberesistedbythe
friction interface between the in-situ topping slab and the
precast biscuit or by the rebar trusses, or both.
Calculationofthelongitudinalshearfollowstheformulafor
Shear Flow:
q = V* Q
I
Where: qisthelongitudinalshear,orshearflow,inkN/mm
V*isthetransverseshearforce(kN)
Qisthefirstmomentofareaattheshearinterface
(mm3)
Iisthemomentofinertiaabovethenaturalaxis
(mm4)
Forinstance,takingtheexamplefromSection4.7.3.wherethe
totalloadontheslabis10.47kPa,andweassumeasinglespan
of7.5mandtributarywidthof6m.
V* = wL
= 10.47 × 6 × 7.5
= 235.5kN
2
2
Ixx = BD3
= 6000 × 0.275 3
= 7812.5 ×106 mm 4
12 12
Q60mm = (60 ×6000) × 250
– 60
= 34.2 × 106 mm 3
2 2
q = 235.5 × 34.2 × 106
= 1.031kN/mm
7812.5 × 106
Ifthelongitudinalshearforcefromtheabovecalculationis
resistedover6mwidthby9rebartrusses,eachwith2xN6
rebarat100mmcentresthentheshearresistanceprovidedby
the trusses is:
ØVlong = 0.8 × 500MPa × 28mm2 × 18 bars
= 2.02kN/m resistance
100 mm spacing
Inthiscasetheshearresistanceoftherebarissufficientto
resist any longitudinal shear forces at the in-situ/precast
interface.
( )
Ifpunchingshearbecomestoogreattobeabletobesupported
bythetoppingslabalone,andshearties/studsareimpractical,
itmayalsobepossibletopouralocalised“mushroomhead”
(Figure26)aroundthecolumn,wheretheprecastslabiscut
backroughly100mmandtheentiredepthofconcreteisused.
Forinstance,takingthepreviousexample,ifdom
were
increasedby60mmto239mm,thentheshearperimeteru
becomes4(500+239)=2956mm.Punchingshearcapacityis
increasedbyapproximately45%
ØVuo=0.7×2956×239×2.15=1063kN
Figure 26 – Punching Shear Setback
4.7.5 Alternatives for Punching Shear
Thedesignercanthendeducethatthecolumntributaryload
areaisapproximately731.7/10.47=69.9m2 that could be
carried by the topping portion of the slab alone with no
punching reinforcing.
IfusingAS3600section9.2.4,therearefurtherreductions
duetothetorsionalmomentsacrossthecolumn,
approximatelyequaltouMv* which need to be considered.
8V* adom
4.7.4 Punching Shear Using Rebar Trusses
ItispossibletoconsiderthefulldepthoftheAustralDeckslab
for punching shear, using the rebar trusses as shear ties.
Generally, the design for this should be undertaken using the
Eurocode provisions, and would require careful checking.
Usually, however, the spacing of the trusses and lack of truss
continuityovercolumnsupportsprecludestheirinclusionin
the punching shear calculations.
Forinstance,a500x500concretecolumnsupportinga
275mmthickN40AustralDeckslabhasthefollowingcapacity
in accordance with AS3600.
ØVuo = Øudom (fcv + 0.3σcp )
fcv = 0.17 1 + 2
√ f’c ≤ 0.34 √ f’c
βh σcp = 0 (slab is not tensioned)
βh = 1 (square column aspect ratio)
fcv = 0.34√40 = 2.15MPa
dom = 179mm 275mm – 30 cover – 12mm
– 60mm planket
2
u = 4 ×(500 + dom ) = 4 × (679) = 2716mm
ØVuo = 0.7 × 2716 × 179 × 2.15 = 731.7kN
Fora275mmAustralDeckslab,carryingresidentialloads
(1kPaSDLand1.5kPaLL)withself-weightof5.85kPa
(basedon15%voidratio),thetotalultimateslabweightis
1.2(5.85+1)+1.5(1.5)=10.47kPa.
(
(
)
)
AUSTRAL PRECAST
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Austral Deck TECHNICAL GUIDE
5.2 Design Criteria and Specifications5.2.1 Strength
ThePanelmustresistthebendingandshearactioneffects
fromalltheappropriateloadcombinations.Inthecaseofa
simplysupportedpanelthefollowingloadcombinationsare
appropriate.
StageI–priortoplacementofconcrete
1.25G+1.5Quv
+1.5M1 (1)
StageII–duringplacementofconcrete
1.25G + 1.25Gc + 1.5Q
uv + 1.5M
2 (2)
1.25G + 1.25Gc + Q
c (3)
StageIII–afterplacementofconcrete
1.25G + 1.25Gc + 1.5Q
uv + 1.5M
3 (4)
Ifthepanelisconsideredaprimarymemberasper
AS3610–1995,thentheseloadsmustbemultiplied
byafactorof1.3.Forexample:
StageI–priortoplacementofconcrete
1.3(1.25G + 1.5Quv
+ 1.5M1)
(5)
5.2.2 Stiffness
Thepanelstiffnessmustbesuchthatthedeformationunder
theappropriateloadcombinationdoesnotexceedchosen
limits,usingeitherthelimitsspecifiedinAS3610.1–2010,
Table3.3.2(Formfacedeflection)orotherwisechosen.In
thecaseofasimplysupportedpanelthefollowingload
combinationsareappropriate:
StageII–duringplacementofconcrete
G + Gc + Q
uv (6)
StageIII–afterplacementofconcrete
G + Gc + Q
uv + M
3 (7)
While AS 3610 – 1995 does not require the addition of Quv
, it
has been added to be in line with the intentions of AS 1170.0
– 2002.
5.2.3 Surface Finish
Thesurfacefinishofthepanelsoffitconformswiththe
physicalqualityofa“Class2”surfacefinishasspecifiedin
AS 3610.1 – 2010. The surface class chosen for the in situ
slabisalsousedtodefinethemaximumallowabledeflection
limits.
5.2.4 Panel Capacity
The strength and stiffness of the panel is dependent on the
truss,panelsizeandgeometry.Duringconstructionthe
appliedloadsareresistedbytheactionofthetrussmembers
andpanelconcrete.Theresistanceprovidedbyanymeshor
additionalreinforcementbarsisignored.
Thefollowingstructuralchecksareperformed:
Themaximumallowablespaniscalculatedforeachcase.
STRENGTH
a)TopChordCompression
b)TopChordTension
c)BottomChordCompression
d)BottomChordTension
e)ConcretePanelCompression
f)DiagonalCompression
g)ConcreteTensileStrength
SERVICEa)Deflection
b)Cracking
5.1 Stage one: Design as formworkTheprecastelementofAustralDeckmustbedesignedas
formworkforconstructionloadssinceitisutilisedas
permanentformwork.Thestrengthoftheprecastelement
requiredtospanbetweentemporaryandpermanentsupports
duringconstructionisgainedfromthelatticegirdertype
reinforcementthatispartiallyembeddedintheprecast
concrete.
Thetopchordofthelatticegirdertypereinforcementisnot
embeddedintheprecastconcretesoAustralDeckmustbe
designedasformworkusingacombinationoftheAustralian
StandardforConcreteStructures(AS3600-2009)andSteel
Structures(AS4100-1998)alongwiththeAustralianstandard
forloading(AS1170)andformwork(AS3610-2010).
Itisrecommendedthatthedesignengineerusesstrict
deflectioncriteriawhendesigningasformworkfor
constructionloadstoalleviateanysignificantcracking.
ThissectionistodemonstratetheprocessofdesigningAustral
Deckasformworkcomplyingwiththestability,strengthand
serviceabilitylimitstagecriteriaspecifiedinAS3610-1-2010
FormworkforConcrete–Part1Documentationandsurface
finish.
Theprocessisusedtodeterminethemaximumspanning
capacity of Austral Deck based on the structural properties
andconstructionloadsinordertodefinethetemporary
proppingrequirementofaconcreteslabconstructedusing
Austral Deck.
Thespecifccalculationsinthisdocumentapplytoasimply
supported double span Austral Deck panel for the variable
structural properties and construction loads listed on 5.3.1.
Howeverthecalculationsalsoprovideguidanceforother
situations.
Charts2and3in5.4.8and5.4.9canbeusedasaguidefor
AustralDeckasformworkunderconstructionloadsfor
variousslabthicknessandsteellatticegirderreinforcement
con gurations.
AustralDeck–ConstructionLoadAnalysissoftwarecanbe
usedtodeterminepropspacingforavarietyofstructural
properties and construction loads.
The software can be downloaded via the Austral Precast
websitewww.australprecast.com.au
5. AUSTRAL DECK DESIGN AS FORMWORK
Figure 27 – Interior Support During Construction
EQUAL SPAN EQUAL SPAN
AUSTRAL PRECAST
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Austral Deck TECHNICAL GUIDE
5.3 Panel PropertiesOverallSlabThickness,d= 250 mm
MinimumCoverto
BottomReinforcement= 20 mm
Concrete Density, r = 2400 kg/m3
ConcreteStrengthatLoading,ƒcm= 20 MPa
Concrete Modulus of Elasticity, Ecj= 22,610 MPa
PanelWidth,b= 2,500 mm
Precast Panel Thickness, tp= 75 mm
NumberofTrussperPanel,nt= 10
NumberofVoids,nv= 0
Void Width, bv= N/A mm
Void Thickness, tv= N/A mm
ClassofSurfaceFinish= 2
NumberofSpans(basedonsupports)= 2
The panel concrete properties (ƒcm, Ecj)areatthetime
ofliftingfromcastingbeds.
5.3.1 Construction Loads
PanelDeadLoad,G= 1.87 kPa
In-situSlabDeadLoad,Gc= 4.29 kPa
ConstructionLiveLoad,Quv = 1 kPa
ConcreteMoundingLoad,Qc= 3 kPa
Stacked Materials, M1= 4 kPa
Stacked Materials, M2= 0 kPa
Stacked Materials, M3= 4 kPa
* Although AS 3610 – 1995 states that the concentrated load Qc
willapplyoveranareaof1.6x1.6m,ithasbeenappliedover the full area of the panel.
** Theloadsfromstackedmaterials,M, mayapplytoonespanonly.
5.3.2 Load Combinations
5.3.3 Design Load
Therefore the design loads are as follows:
Strength,w*= 19.76 kPa
Service, ws= 11.16 kPa
5.3.4 Truss Properties
AustralDeckTrussType,T= T190/12
Average Truss Spacing, Ts= 250 mm
TrussHeight,Th = 192 mm
Truss Bar Yield Strength, fsyt= 500 MPa
5.3.5 Top Chord
BarDiameter,dt= 11.9 mm
Area, At= 1,112.2 mm2
StrutLength,Lt = 200 mm
EffectiveLength,It= 180 mm
Radius of Gyration, rt= 2.98 mm
5.3.6 Bottom Chord
BarDiameter,db= 6.3 mm
Area, Ab= 623.4 mm2
StrutLength,Lb = 200 mm
EffectiveLength,Ib= 200 mm
Radius of Gyration, rb= 1.58 mm
5.3.7 Diagonal Lacing
BarDiameter,dw= 6.3 mm
Area, Aw= 623.4 mm2
Angle ofWeb,q= 62.5 degrees
StrutLength,Lw = 216.5 mm
EffectiveLength,Iw= 151.5 mm
Radius of Gyration, rw= 1.58 mm
5.3.8 Mesh
Mesh= SL72
WireDiameter,dm= 6.8 mm
Area, Am= 448 mm2
STAGE LOAD COMBINATION LOAD UNIT EQUATION
l 1.3 (1.25G + 1.5Quv + 1.5M1)** 12.78 kPa
(5)ll 1.3 (1.25G + 1.25Gc + 1.5Quv+ 1.5M2)** 11.96 kPa
ll 1.3 (1.25G + 1.25Gc + Qc)* 15.86 kPa
lll 1.3 (1.25G + 1.25Gc + 1.5Quv + 1.5M3)** 19.76 kPa
STIFFNESS
ll G + Gc + Quv 7.16 kPa (6)
lll G + Gc + Quv + M3** 11.16 kPa (7)
5.2.5 Maximum Span
Themaximumspanisselectedonthebasisthatthedesign
action,calculatedfromthefactoredloadcombinations,does
not exceed the capacity of the panel.
Asummaryofthecalculationsshowingthemaximumspan
for each action is given in the table below:
DESIGN ACTION MAX SPAN (m)
POSITIVE BENDING
TopChordCompression 3.41
BottomChordTension 3.37
NEGATIVE BENDING
Top Chord Tension 3.95
BottomChordCompression 1.33
ConcretePanelCompression 5.59
SHEAR DiagonalLacingCompression 5.13
CRACKINGConcrete Tensile Strength 2.23
Flexural Cracking 3.96
DEFLECTION ServiceabilityDeflection 3.05
Themaximumspanforthegivenconfigurationistherefore:
Thebottomchordcompressionlimitcanbeignored
ifthebottomchordiscompletelyembeddedinthepanel
concrete for its full length. Control for concrete tension can
also be ignored as it is based on the uniaxial tensile strength
oftheconcretepanelratherthantheflexuraltensile
strength.Thisimpliesthattheconcreteisallowedtocrack
butiscontrolledbythelimitssetoutinSection9.4.1of
AS3600-2009.
5.2.6 Stacked Materials
ThemaximumspanloadingsincludefactorsM1,
M2 and M
3fortheliveloadingsofstackedmaterials.
AS 3610 – 1995 gives these values as 4.0 kPa for before and
aftertheplacementofconcrete(M1 and M
3),and0kPafor
duringtheplacementofconcrete(M2).
Themaximumspanmaybeincreasedbydecreasingthese
loads.Insuchacase,thisloweredloadlimitmustbeclearly
indicatedintheformworkdocumentationandconstruction
controlput in place to ensure it is not exceeded.
5.2.7 Assumptions
1) Verticalandhorizontalactioneffectsfromenvironmental
loadshavebeenignored(e.g.winduplift,rivercurrents).
Ifrelevant,appropriatestrengthandserviceloadsshould
be calculated with reference to AS 3610 – 1995, Table
4.5.2.
2) ThevalueforstackedmaterialsduringStageI(M1)applies
alsotoStageIII(M3)andduringStageIIthevaluefor
stackedmaterials(M2)is0kPa.
3) Theeffectsofformfacedeflectionandconstruction
tolerances can be ignored.
4) Thedeviationsspecifiedforformfacedeflection,
in AS 3610.1 – 2010, Table 3.3.2, will be interpreted
asthedeflectioncriteriaforthepanelasperthefollowing
extract:
5) Theweldsconnectingdiagonalwirestothetop
andbottomchordofthetrussarecapableoftransmitting
the full design action effects.
6) Trussgeometryisasperthefollowingtable:
SURFACE CLASS DEFLECTION LIMIT
1 Lesserof2mmorspan/360
2 Lesserof3mmorspan/270
3 Greaterof3mmorspan/270
4 Greaterof3mmorspan/270
5 N/A
TRUSS TYPE
WIRE SIZE (mm)
TOP BOTTOM DIAGONAL HEIGHT
T90/10 9.5 6.3 6.3 92
T110/10 9.5 6.3 6.3 111
T150/10 9.5 6.3 6.3 154
T190/10 9.5 6.3 6.3 191
T110/12 11.9 6.3 6.3 112
T150/12 11.9 6.3 6.3 155
T190/12 11.9 6.3 6.3 192
MaximumSpan 3.05m
AUSTRAL PRECAST
/ 40 / / 41 /
Austral Deck TECHNICAL GUIDE
5.4 Panel Properties5.4.1 Diagonal Lacing CompressionWhere Φ= 0.90
FormFactor,kf= 1.00
Section Capacity, Ns=k
fA
nf
y= 311.72 kN
λn= 136.07
aa= 13.93
ab= 0.50
λ= 143.03
η= 0.42
ξ= 0.78
ac= 0.32
LimitStateCapacity,ΦacN
s = 89.21 kN
MaximumSpanbasedonshear
CapacityofDiagonalLacing,Lds= 5.13 m
Themaximumspanuscalculatedfromthegreatestshearat
any point along the slab:
V*=j3w*L L=
Where j3 is a constant that depends
onthenumberofspans.
Steel Elastic Modulus, Es= 200,000 MPa
Concrete Elastic Modulus, Ecj= 22,610 MPa
ModularRatio,n= 8.85
DistancefromSoffittoTopChord= 221.9 mm
TransformedTopChordArea= 9,838 mm2
DistancefromSoffittoBottomChord= 29.9 mm
TransformedBottomChordArea= 4,891 mm2
PanelConcreteArea= 187,500 mm2
Distance to the Neutral Axis, yg= 46.29 mm
SecondMomentofInertia,Ig= 4.07E+08 mm4
NO. OF SPANS j3
1 0.5
2 0.625
≥3 0.6
Largestreinforcementdiameter,db= 6.8 mm
SteelStressLimit,σsteel= 362.3 MPa
AreaofBottomChordSteel,Ab= 623.4 mm2
Area of Mesh Steel, Am= 447.5 mm2
TotalAreaofBottomSteel= 1,071 mm2
EquivalentAxialForce,N*= 387.99 kN
TrussHeight,Th= 192 mm
Limitstatemoment
capacity for Steel Stress, M*pf.s= 74.49 kN.m
MaximumSpanbased
onFlexuralCracking= 3.96 m
InaccordancewithAS3600–2009ConcreteStructures,
Clause8.1.3:
ConcreteStrengthatLoading,f'c= 20 MPa
Concrete Strength Factor, a2= 0.85
CompressiveAreaFactor, γ= 0.85
Φ= 0.60
Effective Cross Section Depth
(equal to panel thickness tp),d= 75 mm
yg= 46.29 mm
ku= 0.62
LimitStateCapacity,ΦNc= 1,003 kN
TrussHeight,Th= 192 mm
LimitStateMomentCapacity,M*pc= 192.6 kN.m
MaximumSpanbasedonmoment
capacityofTopChordintension,Lpc= 5.59 m
5.4.5 Crack Control for Flexure
AS3600–2009,Clause9.4.1statestherequirementsfor
crackcontrolinflexuretobedeemedcontrolled.Part(c)
providesalimitbasedonthesteelstress,whichisusedto
defineanothermaximumspanlimit.
5.4.3 Control for Concrete Tensile Strength
AS3600–2009,Clause3.1.1.3definesthetensilestrengthfora
givenconcretemember,thishasbeenusedtoensurethatthe
deflectioncalculationsareaccuratewithoutusingthecracked
secondmomentofarea.
M*pt
= wheref'ct.f=0.6√ f'
c
f'ct.f= 2.68 MPa
LimitStateMomentCapacityfor
concrete strength, M*pt= 23.61 kN.m
MaximumSpanbasedoncontrolling
toconcretetensilestrength,Lpt= 2.23 m
V*j
3w
f'ct.f
'Ig
yg
5.4.2 Concrete Panel Compression
Transformed Section:
Forserviceabilitylimitstate,thepanelisanalysedasan
uncrackedsectionusingtheTransformedAreamethodto
determinethestressesinthesteelandconcrete.
5.3.9 Capacity Calculations
Thenumberofspans(basedonthenumberoftemporary
supports)affectsthecoefficientsusedwhencalculatingthe
maximumspans:
M*=jw*L L=
5.3.10 Top Chord Compression
InaccordancewithAS4100–1998SteelStructures,
Clause 7.1 – N*≤Φag N
2
NO. OF SPANS j1, POSITIVE MOMENT
j2, NEGATIVE MOMENT
1 0.125 N/A
2 0.096 0.125
≥3 0.101 0.121
WhereΦ= 0.9
FormFactor,kf= 1
Section Capacity, Ns=k
f A
nf
y = 556.1 kN
λn= 85.57
aa= 18.77
ab= 0.50
λ= 94.95
η= 0.27
ξ= 1.07
ac= 0.58
LimitStateCapacity,ΦacNs = 288 kN
TrussHeight,Th = 192 mm
LimitStateMomentCapacity,M*tc = 55.28 kN.m
MaximumSpanbasedon
MomentCapacityofTopChord
incompression,Ltc = 3.41 m
WhereΦ= 0.9
FormFactorkf= 1
Section Capacity, Ns=k
f A
nf
y = 311.7 kN
λn= 179.6
aa= 11.05
ab= 0.50
λ= 185.11
η= 0.56
ξ= 0.68
ac= 0.20
LimitStateCapacity,ΦacNs = 56.88 kN
TrussHeight,Th = 192 mm
LimitStateMomentCapacity,M*bc
= 10.92 kN.m
MaximumSpanbasedon
MomentCapacityofTopChord
incompression,Lbc
= 1.33 m
WhereΦ= 0.9
LimitStateCapacity,ΦAgf
y= 500 kN
TrussHeight,Th = 192 mm
LimitStateMomentCapacity,M*tt= 96.09 kN.m
MaximumSpanbasedonMoment
CapacityofTopChordintension,Ltt= 3.95 m
5.3.11 Top Chord Tension
InaccordancewithAS4100–1998SteelStructures,
Clause 7.1 – N*≤ΦAgf
y
5.3.13 Bottom Chord Tension
InaccordancewithAS4100–1998SteelStructures,
Clause 7.1 – N*≤ΦAgfy
5.3.12 Bottom Chord Compression
InaccordancewithAS4100–1998SteelStructures,
Clause 6.1 – N*≤ΦacNs
Where Φ= 0.9
LimitStateCapacity,ΦAgf
y= 281 kN
TrussHeight,Th = 192 mm
LimitStateMomentCapacity,M*bt= 53.87 kN.m
MaximumSpanbasedonMoment
CapacityofTopChordintension,Lbt= 3.37 m
M*jW*
2
AUSTRAL PRECAST
/ 42 / / 43 /
Austral Deck TECHNICAL GUIDE
5.4.8 Single Span
Variables:75mmprecast,fcmi20MPa,SL72mesh,20cover,Class2finish.
0
50
100
150
200
250
300
350
400
450
500
00.5 1 1.5 2 2.5 3.53
Maximum Distance between Supports (m)
T80/10, 250 spacing
T80/10, 565 spacing
T110/10, 250 spacing
T110/10, 565 spacing
T150/10, 250 spacing
T150/10, 565 spacing
T110/12, 250 spacing
T110/12, 565 spacing
T150/12, 250 spacing
T150/12, 565 spacing
T190/12, 250 spacing
Tota
l Co
nc
rete
Sla
b T
hic
kne
ss (
mm
)
0
50
100
150
200
250
300
350
400
450
500
00.5 1 1.5 2 2.5 3.53
Maximum Distance between Supports (m)
T90/10, 250 spacing
T90/10, 565 spacing
T110/10, 250 spacing
T110/10, 565 spacing
T150/10, 250 spacing
T150/10, 565 spacing
T110/12, 250 spacing
T110/12, 565 spacing
T150/12, 250 spacing
T150/12, 565 spacing
T190/12, 250 spacing
T190/12, 565 spacingTota
l Co
nc
rete
Sla
b T
hic
kne
ss (
mm
)
0
50
100
150
200
250
300
350
400
450
500
00.5 1 1.5 2 2.5 3.53
Maximum Distance between Supports (m)
T80/10, 250 spacing
T80/10, 565 spacing
T110/10, 250 spacing
T110/10, 565 spacing
T150/10, 250 spacing
T150/10, 565 spacing
T110/12, 250 spacing
T110/12, 565 spacing
T150/12, 250 spacing
T150/12, 565 spacing
T190/12, 250 spacing
Tota
l Co
nc
rete
Sla
b T
hic
kne
ss (
mm
)0
50
100
150
200
250
300
350
400
450
500
00.5 1 1.5 2 2.5 3.53
Maximum Distance between Supports (m)
T90/10, 250 spacing
T90/10, 565 spacing
T110/10, 250 spacing
T110/10, 565 spacing
T150/10, 250 spacing
T150/10, 565 spacing
T110/12, 250 spacing
T110/12, 565 spacing
T150/12, 250 spacing
T150/12, 565 spacing
T190/12, 250 spacing
T190/12, 565 spacingTota
l Co
nc
rete
Sla
b T
hic
kne
ss (
mm
)
5.4.9 Two Span
Variables:75mmprecast,fcmi20MPa,SL72mesh,20cover,Class2finish.
** TheinformationinthegraphshasbeengeneratedinaccordancewithAustralianStandard™.Formworkforconcrete.AS3610AS3610-1995FormworkforConcreteandAS3610.1-2010Formworkforconcrete–Part1Documentationandsurfacefinish
* Theinformationinthegraphsareindicative,shouldbeusedasaguideonlyanddoesnotreplacetheneedforqualifiedstructuraldesignengineer.
Chart 2 – Maximum distance between supports for single span
Chart 3 – Maximum distance between supports for multi span
5.4.6 Deflection
Themaximumdeflectionofthepanelcanbecalculatedfrom
either of the following questions:
Foranabsolutevalueofadeflectionlimit,
∆= L=√Where j
4isavaluethatvariesbasedonthenumberofspans
and ∆isthedeflectionlimit.Foraspan:deflectionratio
limit,
= L=√Where j
4isavaluethatvariesbasedonthenumberofspans
and βisthespan:deflectionrationlimit.
Astheprecastslabinassumedtobecrackedfordeflection
calculation,onlythesteeltrussmembersareusedforthe
values of E and I.Anyreinforcingmeshisnottreatedas
contributingtodeflectioncontrolasitisnotassumedtobe
sufficientlyattachedtothetrussframes.
NO. OF SPANS j4
1 0.0130
2 0.0092
≥3 0.0099
Surfacequalityclass= 2
Maximumdeflection(absolute)= 3 mm
Maximumdeflection(ration),ß= 270
Area of tensile steel, Ast= 623.4 mm2
Distance of tensile steel, dst= 29.9 mm
Areaofcomprehensivesteel,Asc= 1,112.2 mm2
Distancetocomprehensivesteel,dsc= 221.9 mm
Neutral axis height for
steel truss only, dsn= 152.9 mm
Secondmomentofinertia
forsteeltrussonly,Is= 1.47E+07 mm4
Maximumspanbased
onabsolutelimit,Ldef.abs
= 3.05 m
Maximumspanbased
onrationlimit,Ldef,rat
= 4.74 m
Maximumspanbased
onserviceabilitylimits,Ldef= 3.05 m
5.4.7 Maximum Spans Summary
Topchordcompressionlimit= 3.41 m
Topchordtensionlimit= 3.95 m
Bottomchordcompressionlimit= 1.33 m
Bottomchordtensionlimit= 3.37 m
Diagonallacingcompressionlimit= 5.59 m
Concretepanelcompressionlimit= 5.13 m
Concretetensioncontrollimit= 2.23 m
Flexuralcrackinglimit= 3.96 m
Deflectionlimit= 3.05 m
Governing limit = 1.33 m
Governing limit, ignoring bottom chord compression and flexural cracking = 3.05 m
Whenchoosingthemaximumallowablespan,thebottom
chordcompressionlimitmaybeignoredinsomesituations.
Thebottomchordcompressionlimitcanbeignoreifthe
bottomconcretepanelisassumedtoprovidesufficient
restrainttopreventbuckling.Whenchoosingthemaximum
allowablespan,theconcretetensioncontrollimitmaybe
ignored.Thislimitmaybeignoredasitisbasedonthe
uniaxial tensile strength of the concrete panel, as opposed to
theflexuraltensilestrength.Astheprecastpanelisnot
typically going to be axially loaded, this is not relevant.
Thehorizontalloadingoftheframework(AS3610–1995,
Clause4.4.5)mustalsobeprovidedfor.Thiswilltypicallybe
aroleoftheedgeformdesigner.
j4w
sL ∆EI
EI j4w
s
4
j4w
sLL
EIβ
EI
βj4w
s
3
AUSTRAL PRECAST
/ 44 / / 45 /
Austral Deck TECHNICAL GUIDE
Figure 29 – Primary positive moment (about R axis)
Figure 30 – Primary negative moment (about R axis)
Figure 31 – Secondary positive moment (about S axis)
Figure 32 – Secondary negative moment (about S axis)
6.1 Sensitivity Analysis of Two-Way Slabs – Example 1
Theexamplebelowisanexampleofthechangesforasimple
two-wayslabspanningmultiplegrids.Threecasesforthe
exampleareproduced:
•Case1:Idealised2-waystiffness(KMr=KMs=1)
•Case2:75%two-waystiffness(KMr=1,KMs=0.75)
•Case3:50%two-waystiffness(KMr=1,KMs=0.50)
Theexampleuses:
•2x2spansof6.5mbetweencolumns
•300x300concretecolumns
•3kPaLiveLoadand1.5kPaSuperimposedDeadLoad(SIDL)
•250mmAustralDeckslabswith17%weightreduction
•Defaultvaluesforcreepandshrinkagecoefficients
•30yearloadhistoryforcrackedsectiondeflection
calculations
TheslabisorientatedsuchthatRisLeft-RightandSis
Up-Downonthepage.ReducingKMseffectivelyreduces
stiffness about the S direction. This is the equivalent of the
planksorientatedintheUp-Downdirection.Forthisexample,
theremightbe2plankspansintheup-downdirection,but
5-6spansintheLeft-Rightdirection.
The results indicate the following:
Astheaboveexampleisonly2x2spans,thereisonlylimited
optionsformomentredistribution,buttheresultsstill
indicateincreaseddeflectionsupto50%andredistributionof
secondarymomentsintoprimarymoments.
Resultswouldalsobemorepronouncedforrectangulargrid
layouts,suchas6mx8.5m,ratherthansquaregridlayouts,
whichdonotnaturallylendthemselvestoprimaryand
secondary span directions.
The following screen captures are results on the above
options.
6. EXAMPLE MODELS AND CALCULATIONS
Table 9 – Differential stiffness results for Three Austral Deck slabs
Figure 28 – Long term (30 year) deflection for 100%, 75% and 50% secondary stiffness
Design Case Idealised 2-way 75% Secondary Stiffness 50% Secondary Stiffness
Mid-span Deflection 31.5mm 36.1mm 46.7mm
Primary +ve Moment 38.1kNm 41.1kNm 44.6kNm
Primary -ve Moment -117kNm -120kNm -138kNm
Secondary +ve Moment 38.1kNm 37.8kNm 36.6kNm
Secondary -ve Moment -120kNm -104kNm -101kNm
AUSTRAL PRECAST
/ 46 / / 47 /
Austral Deck TECHNICAL GUIDE
6.2.1 Strip 1 – Vertical Span
Theabovestripis230thick,with2equalspansof6.5.It
carriestributarywidthofapproximately7.5m,butinpractice
thisamountisreducedduetothesemi-two-waynatureofthe
slab.
Thebendingmomentdiagramfortheaboveslabisasfollows:
Themaximumpositivestripbendingmomentforthedesign
stripis110kNmoverthe2.5mplankwidth,or44.0kNm.
Tosatisfythismoment,reinforcementof630mm2/mis
needed, as follows:
ØMuo = 0.8 ∙ Ast ∙ fsy ∙ d - Ast ∙ fsy
2 ∙ 0.85 ∙ b ∙ f 'c
= 0.8 ∙ 800 ∙ 500 ∙ (194 - 630 ∙ 500
2 ∙ 0.85 ∙ 1000 ∙ 40
= 47.72kNm > 44.0kNm
630mm2/mcanbesuppliedasN12barsat200mmcentres
(565mm2/m)laidontopofSL92mesh(287mm2/m),ortotal
852mm2/m.
Theneutralaxisdepth,194mm,isbasedonthetotalslab
depth:
d = 230 - 30 (cover) - 6 N12 bar
= 194mm
2
Negativemomentoverthecolumnsis243kNm/mover2.5m
width.
Thiscanbeprovidedwith3450mm2reinforcinginasimilar
way,withatraditionalreinforcinglayoutover2.5m:
ØMuo = 0.8 ∙ Ast ∙ fsy ∙ d - Ast ∙ fsy
2 ∙ 0.85 ∙ b ∙ f 'c
= 0.8∙ 3350 ∙ 500 ∙ 194 - 3350 ∙ 500
2 ∙ 0.85 ∙ 2500 ∙ 40
= 244.08kNm > 243kNm
3,350mm2canbesuppliedby17xN16bars,orN16at150mm
centresover2.5mwidth.
Figure 34 – Example Slab
(
(
((
()
)
))
)
6.2 Worked CalculationsUsingtheexamplemodelfromsection3.3,somefurther
workedcalculationsaretakenbelow.Inthiscase,the
bathroomsetdownsareremovedforsimplicity.
The design loads and slab features are as follows:
Twofulldesignstripswillbetakenasexamples,highlighted
above in Red.
Figure 33 – Example Slab
Design Properties Value
GeneralLoading Residential
SuperimposedDeadLoad 1.0kPa
LiveLoad 2.0kPa
Slab Thickness 230mm
Precast Thickness 60mm
Columns 400x400
Shrinkage Restraint 11%(Minimalwalls)
AUSTRAL PRECAST
/ 48 / / 49 /
Austral Deck TECHNICAL GUIDE
6.2.5 Check on Punching Shear
Punchingshearchecksarefirstcompletedagainstthein-situ
portion of the slab.
Inthecaseofthecentralcolumnintheaboveexample,the
punching shear forces are:
Firstcheckthein-situportion(D=160mm,dom=125mm)in
accordance with AS3600:
f 'cv = 0.17 1 + 2
√f 'c ≤ 0.34 √f 'c (but βh = 1)
βh f 'cv = 0.34 √f 'c = 2.15MPa
dom = 125, u = 4 ∙ (400+125) = 2100mm
ØVuo = 0.7 ∙ 125 ∙ 2100 ∙ 2.15 = 395kN < 584kN (fail)
Nexttrythefulldepth(D=230mm,dom=195mm):
dom = 195, u = 4 ∙ (400 + 195) = 2380mm
ØVuo = 0.7 ∙ 1 95 ∙ 2380 ∙ 2.15 = 698kN > 584kN (OK)
Checktorsionstripreduction,(a=400+195=595mm)
ØVu = ØVuo 1.0 + u ∙ Mv*
8V* ∙ a ∙ dom ØVu = ØVuo 1.0 +
1.0 + 2380 ∙ 32.3 584 ∙ 595 ∙ 195
ØVu = 698 1.0 +
2380 ∙ 32.3 × 103 8 ∙ 584 ∙ 595 ∙1 95
ØVu = 698 1.1418 = 611.3kN (OK)
As punching shear fails on the in-situ portion alone, but
passes when including the precast portion, the designer
should ensure that the total reinforcing bars in the trusses are
sufficientto“hangup”theloadbetweentheprecastand
in-situportionsoftheslab.Ifnot,thenshearstudsshouldbe
considered.
(
(( (
)
) ) )
Punching Shear Reactions Value
V* 584kN
Mr* 0.02kNm
Ms* 32.3kN
Ms* 32.3kN
6.2.2 Strip 2 – Horizontal Span
SimilartoStrip1,thepositivemomentsare100,50.9and
65.7kNminthedesignstripspans1to3respectively.
WetakeSpan1asanisolatedplank,andachievethemoments
thus:
ØMuo = 0.8 ∙ Ast ∙ fsy ∙ d - Ast ∙ fsy
2 ∙ 0.85 ∙ b ∙ f 'c
= 0.8 ∙ 1350 ∙ 500 ∙ 194 - 1350 ∙ 500
2 ∙ 0.85 ∙ 2500 ∙ 40
= 102.6kNm > 100kNm
1350mm2isprovidedbyN12at250mmcentresplusSL92
mesh.
Forspans2and3,weuse65.7kNmasthecriticalmoment,
whichisachievedwithN12at300mmcentres.
Thenegativemomentforthehorizontalspanis210kNmand
151kNmatthetwointernalcolumns.
ØMuo = 0.8 ∙ Ast ∙ fsy ∙ d - Ast ∙ fsy
2∙ 0.85 ∙ b ∙ f 'c
= 0.8 ∙ 3350 ∙ 500 ∙ 180 - 3350 ∙ 500
2∙0.85∙2500∙40
= 228.06kNm > 210kNm
Notethereducedcoverd=180mm,forthesecondlayerof
rebar.
Thismomentisresistedby3,350mm2orN16at150mm
centresover2500mm.
Inthecentralportion,thewidthis2xD+Column,
=2x230mm+400mm=860mm.
Over860mm,N16-150mmis1152mm2,whichprovides
momentof
ØMuo = 78.5kNm < 84.5kNm.
This fails clause 9.1.2.
The designer can choose either to increase the reinforcing in
thislocation,ortoclosethebarcentresoverthecolumn.
6.2.4 Check on Secondary Moment Direction
Thesecondarynegativemomentsarenotaddressedinthis
example,asthereinforcingbarsarelaidtraditionallyatthe
top and 2nd layers.
Thesecondarypositivemoments,however,canonlybe
resistedbytheSL92meshcaseintheprecastplank,plusextra
barslaidontopoftheprecastatreducedcover(60mm).
Inthisexample,thesecondarymomentis40.8kNmover
2.5m.
ThemomentcapacityintheplankusingSL92mesh
(287mm2/m)is:
ØMuo = 0.8 ∙ Ast ∙ fsy ∙ d - Ast ∙ fsy
2 ∙ 0.85 ∙ b∙ f 'c
= 0.8 ∙ 287 ∙ 2.5 ∙ 500 ∙ 194 - 287 ∙ 2.5 ∙ 500
2∙0.85∙2500∙40
= 55.6kNm > 40.8kNm
However,therearebreaksintheplanksevery2.5m.
To account for the breaks, “cracker” bars are placed over the
breaks,whichhavecoverofapproximately70mmtothebar
centre(d=230-65-12/2=159mm)
ThecrackerbarsshouldbeN12at400mmcentres(700mm2
over2500mm):
ØMuo = 0.8 ∙ Ast ∙ fsy ∙ d - Ast ∙ fsy
2 ∙ 0.85 ∙ b ∙ f 'c
= 0.8 ∙ 700 ∙ 500 ∙ 159 - 700 ∙ 500
2 ∙ 0.85 ∙ 2500 ∙ 40
= 44kNm > 40.8kNm
SocrackerbarsofN12at400mmcentresareplaced,centred
over the plank joints.
The cracker bars should be at least one splice-length each side
ofthejoint,orapproximately1200-1500mmintotal.
6.2.3 Check on Column Strip Width
Asalloftheabovestriprunsareconsideredcolumnstrips,
check that the strip width allocation is appropriate with
AS3600.
Inthiscase,thebottomreinforcingissuitable(withthe
columnstripbeing2500mmwide)butthetopreinforcingwill
fail clause 9.1.2, which states:
In two-way flat slabs, at least 25% of the total of the design negative moment in a column-strip and adjacent half middle-strips shall be resisted by reinforcement or tendons or both, located in a cross-section of slab centred on the column and of a width equal to twice the overall depth of the slab or drop panel plus the width of the column.
Forthisexample,inthehorizontalspan,thetotalcolumn
momentrequirementis:
(
(
( (
(
((
()
)
))
)
))
)
(210 + 64 + 64) × 25% = 84.5kNm
AUSTRAL PRECAST
/ 50 / / 51 /
Austral Deck TECHNICAL GUIDE
7.1 Fire Resistance Period7.1.1. Austral Deck ProfileAnyconcreteslabmustbedesignedtoachieveafire
resistance period(1)(FRP)forstructuraladequacy,integrity
andinsulationofnotlessthantherequiredfireresistance
level(2)(FRL)asspecifiedinTheNationalConstructionCode
–BuildingCodeofAustralia(NCC-BCA).
Chart 4 shows FRP for insulation of various slab thicknesses
constructed using Austral Deck. The FRP has been
calculated in accordance with Australian Standards:
Concrete Structures, AS3600-2009, Clause 5.2.1 –
Insulationforslabs,andmodifiedtakingintoaccount
AustralDeckprofile–Figure35and36.
Chart 4 – Fire Resistance Period(3) for insulation for solid slabs constructed using Austral Deck profile.
30min
50mm
100mm
150mm
200mm
250mm
60min 90min
FRP “minutes”
Min
imu
m S
lab
Thic
kne
ss “
mm
”
120min 180min 240min
30min
50mm
100mm
150mm
200mm
250mm
60min 90min
FRP “minutes”
Min
imu
m S
lab
Thic
kne
ss “
mm
”
120min 180min 240min
Figure 35 – Austral Deck side profile.
Figure 36 – Effective thickness for FRP calculation Austral Deck profile.
Effective thicknessfor FRP Calculation
Min
sla
bth
ickn
ess
Austral Deck
20
10
2410
16
60, 7
5, 9
0
Effective thicknessfor FRP Calculation(without joint sealant)
Austral Deck Flat pro�le
Min
sla
bth
ickn
ess
Effective thicknessfor FRP Calculation
Min
sla
bth
ickn
ess
Austral Deck
20
10
2410
16
60, 7
5, 9
0
Effective thicknessfor FRP Calculation(without joint sealant)
Austral Deck Flat pro�le
Min
sla
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7.1.2. Thermal ResistanceAustral Deck, as part of the concrete slab can be designed to
achieveenergyefficiencyprovisionsasspecifiedinThe
NationalConstructionCodeVolumeTwo–BuildingCodeof
Australia(BCA).
TheThermalresistancecoefficient“TheR-Value”(4)ofthe
Austral Deck slab is affected by the precast panel thickness,
overall slab thickness, the use of slab voids, the use of other
insulationmaterials,flooringandceilingmaterial.
TheNationalPrecastConcreteAssociationofAustralia(5)
“NPCAA” has developed a software to calculate the R Value
of Austral Deck considering all the above factors. Copy of the
software can be downloaded via the NPCAA website:
www.nationalprecast.com.au/r_value_calculator/
7.1.3. Definitions and References(1)Fireresistanceperiod(FRP)
Time,inminutes,foramembertoreachtheappropriate
failure criterion (i.e., structural adequacy, integrity and/or
insulation)iftestedforfireinaccordancewiththe
appropriate Standard. Source Australian Standards,
Concrete Structures, AS3600-2009, Clause 5.2.5
(2)Fireresistancelevel(FRL)
Fire resistance periods for structural adequacy, integrity and
insulation, expressed in that order.
NOTE: Fire resistance levels for structures, parts and
elementsofconstructionarespecifiedbytherelevant
authority,e.g.,intheBuildingCodeofAustralia(BCA).
Source Australian Standards, Concrete Structures, AS3600-
2009, Clause 5.2.4
(3)Section5ofAS3600-2009outlinestherequirementsfor
thefireresistanceofslabs.Itisassumedthatthecriteriafor
integrityisconsideredtobesatisfiedifthedesignmeetsthe
criteria for both insulation and structural adequacy for that
fireresistanceperiodasperclause5.3.1ofAS3600-2009
(4)TheR-valueofasubstanceisitsdirectmeasureofits
resistancetotransferringenergyorheat;RValuesare
expressedusingthemetricunits(m2.K/W).Theamountof
degreeskelvintemperaturedifferencerequiredtotransfer
onewattofenergyperonesquaremeterofasubstance.
(5)PublishedwithanapprovalfromNPCAA
7. FIRE AND THERMAL RESISTANCE
AUSTRAL PRECAST
/ 52 / / 53 /
Austral Deck TECHNICAL GUIDE
8.1.3. End Support to Internal Precast Wall
8.1.2. End Support to External Precast Wall – Option 2
8. TYPICAL INSTALLATION DETAILS
8.1.1. End Support to External Precast Wall – Option 1
8.1 Typical Wall Connection – End Support
Figure 37
Figure 38
Figure 39
AUSTRAL PRECAST
/ 54 / / 55 /
Austral Deck TECHNICAL GUIDE
8.3.2. Mid Span – Internal Precast Wall Above
8.3.3. End Support – Double Wall Connection
8.4.1. Beam Reinforcement within Slab Thickness
8.4 Typical Beam Configuration
8.2.1. Longitude Side to External Precast Wall
8.2.2. Side Joint Details
Austral Deck side profile.
Effective thicknessfor FRP Calculation
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Austral Deck
20
10
2410
16
60, 7
5, 9
0
Effective thicknessfor FRP Calculation(without joint sealant)
Austral Deck Flat pro�le
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Effective thicknessfor FRP Calculation
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Austral Deck
20
10
2410
16
60, 7
5, 9
0
Austral Deck
Onsite caulking if required (by others)
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8.3.1. End Support – Internal Precast Wall Under
8.2 Typical Wall Connection – Longitudinal Side
8.3 Typical Wall Connection – Internal Precast Wall and Double Wall
Figure 40
Figure 41
Figure 42
Figure 43
Figure 44
AUSTRAL PRECAST
/ 56 /
Austral Deck TECHNICAL GUIDE
85.1. Balcony and Cantilever Arrangement
8.5.2. External Precast Wall with Balcony
8.5 Balcony and Cantilever Arrangement
/ 57 /
8.4.2. Precast Beam
8.4.3. Band Beam formed by Austral Deck
Figure 45
Figure 46
Figure 47
Figure 48
AUSTRAL PRECAST
/ 58 / / 59 /
Austral Deck TECHNICAL GUIDE
Theproppingdesignisprovidedandshallbecertifiedbythe
supplieroftheprops.Thepropswillbecertifiedtocarrythe
definedconstructionloads.
Precast Shell BeamAustral Deck
Precast Shell Beam
Span Direction
Austral Deck
8.6 Proposed Propping Arrangement
Figure 49
Sydney CBD
Ground Floor 50 Carrington Street, Sydney NSW 2000
Melbourne
490 Swan Street Richmond VIC3121
Adelaide
Ground Floor 70HindmarshSquare , Adelaide SA 5000
Brisbane
27JamesStreet Fortitude Valley QLD4006
Perth
67KingStreet Perth WA 6000
Hobart
9 Franklin Wharf Hobart TAS 7000
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