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TRANSCRIPT
APPROPRIATE SELECTION OF METAL THICKNESS FOR USE IN WALLING AND ROOFING APPLICATIONS
CI/SfB
Rh2(4-)
SEPTEMBER 2010
MCRMA Technical Paper No. 20
Contents
Page
Foreword 2
1.0 Summary 2
2.0 Introduction 3
3.0 Nominalthickness/gauge 4
3.1 Steel 4
3.2 Aluminium 4
4.0 Normalrangeofthicknesses 4
5.0 Commonlyusedcoilwidths 5
6.0 Yieldstrengths–constructionpurposes 5
7.0 Tolerancespecification–potentialfornon-compliance 6
7.1 Steel 6
7.1.1 Roofingweathersheet 6
7.1.2 Wallingweathersheet 6
7.2 Aluminiumweathersheet 7
7.3 Flashings 7
7.4 Linersheet 8
8.0 Measuringthethicknessofacoilorsheet 9
9.0 CEMarking–ensuringthatthecorrectmaterialisdelivered 10
10.0 Safeworkingloadasafunctionofmaterialthickness 10
11.0 Useofloadspantables 11
11.1 Nonfragility 11
11.2 Walkability 11
11.3 Useofloadspantables 11
12.0 Profileshape 12
13.0 Fixingregime 13
14.0 Fireperformance 13
14.1 Roofingapplications 13
14.2 Wallingapplications 13
15.0 Interactionwithotherbuildingcomponents 14
16.0 Conclusions 14
17.0 Bibliography 15
©TheMetalCladding&RoofingManufacturersAssociationLimitedandEngineeredPanelsinConstructionLimited.September2010
Foruptodateinformationonmetalroofandwallcladding,includingdownloadableconstructiondetails,visitwww.mcrma.co.uk.
Theeffectofthickness(gauge)ontheperformanceofmetalsystemsinbuildingapplicationscannotbeunder-estimatedandtheresponsibilityfornotonlyensuringthatappropriatematerialsarespecified,butselectedandusedcorrectlyisplaceduponallpartieswithinthesupplychain.
Withregardtotheselectionofcoilorsheetforuseinroll-formingapplicationsitisofparticularimportancethatthematerialselectedandusedcompliesfullywiththeappropriatestandardsoftoleranceondimensionandshape:BSEN10143:2006forpre-finishedsteelandBSEN485Part4forcoldrolledaluminiumwithnormaltoleranceasaminimumrequirement.
Forthosespecifyingandusingmaterialsthekeypointsmustbe:-
• Tostatethestandardthatistoapply.• Ensurethatthematerialtobeorderedandused:-
• Meetstherequirementsofthestandard.• Isdeliveredcorrectly.
• Ensurethatthestructuralcalculationsusedarespecifictotheprofileproposedandthenominalthicknessofthematerialproposed.
• Ensurethatthereactiontofireperformanceisvalidforthenominalthicknessofthematerialproposed.
Theuseofmetalforroofingandwallingapplicationshas,throughstructuralcalculationandoveraperiodofsuccessfulperformanceinservice,determinedthosethicknessesofmaterialwhicharenormallyspecified.
Theperformanceofthesematerialsinuse(includingtheconstructionphase)isdeterminedbyloadingarisingfrompositiveandnegativeforces,wind,deadweightandpointloadorimpact,withthemainrequirementsbeing:-
• Safetyinuse.• Weatherproofing
• Waterpenetration• Airtightness• Robustdetails
• Appearanceandabilitytomaintaininthelongterm.
Usingmaterialswhichvarybeyondthelimitsofthetolerancesallowedintroducesthepossibilitythatthebuildingdesignperformancewillnotbemetand,althoughthismayresultinshorttermsavings,couldaddconsiderablytothewholelifecostsofthebuildingthroughpoorperformanceandpotentialforremedialworksorworse.
TheMetalCladdingandRoofingManufacturersAssociationrepresentsleadingmanufacturersinthemetalroofingandcladdingindustryandseekstofosteranddevelopabetterunderstandingamongstspecifiersandendusersalikeofthemosteffectiveuseofmetalbuildingproducts,componentsandsystems.
TheAssociationhastwomainobjectives:-
1. TomakesurethatpublishedstandardsintheUKandEuropeformetalroofandwallcladdingareinaccordancewithbestpracticesoastoensureaEuropean-widestandardofproductexcellencewhichcanbewrittenintoproductspecifications.
2. Toprovideabasisfortechnicalexcellenceencompassingproductdevelopment,componentanddetaildesign,improvedmanufacturingandco-operationoninstallationtechniquesandstandards
2
Foreword 1.0 Summary
3
ItistheclearlystatedpositionoftheMCRMAanditsmembersthatthebestassuranceofcompliancewiththeappropriatestandardsandperformanceexpectationistosourcesystemsandproductsfromreputablemanufacturerswhocandemonstratethepedigreeofthematerialsusedandsupportdesignrequirementswithjobspecificdata.
Metalcladdingsystemsprovideanefficient,attractiveandreliablesolutionforawidevarietyofexternalbuildingenvelopes.Overtheyearstheyhaveevolvedfromthesingle-skinmetalcladdingoftenassociatedwithagriculturalbuildingstosophisticatedsystemswhichareusedinindustrial,retailandleisureapplicationsthroughouttheUnitedKingdom.
However,aswithallconstructioncomponents,theabilityofthecladdingtosatisfyitsfunctionalrequirementsisdependentonitscorrectspecificationandinstallationand,equallyasimportant,onitsinteractionwiththeotherelementsofthebuildingenvelopeandstructure.
Inthecontinuingquestforimprovedcosteffectivenessinallformsofbusinessgenerallyandconstructioninparticular,combinedwiththeneedtomeetbudgetaryconstraints,theconsiderationofalternativemethodsandchoiceofmaterialstomeetaspecifieddesiredoutcomeisavalidandnecessaryprocessthatmustbeundertaken.Thecompletedcostofconstructionisdirectlyimpactedbythecostsofmaterialsusedwithintheconstructionprocess.
Itiskey,however,ineachstepofthisprocesstounderstandthatanyonechoiceofamaterialtypeorcomponentdoesnotexistinisolationandhaspotentiallywiderreachingimplicationsonotheraspectsoftheperformanceofthecompletedwhole.
Theindividualcomponentsthatmakeupthecladdingsystemareoftenspecifiedandsuppliedseparately,withthepotentialforinsufficientattentionbeingpaidtothewayinwhichtheyinteract.
Thispaperwillfocusonthepotentialeffectsofseekingtoreducetheeffectivegaugeofasteelsheetusedinthemanufactureofanexternalcladdingsystem.
Itwillconsiderthefollowing:-
• Nominalthicknessandadherencetotherelevantstandards.
• Tolerancespecificationandthepotentialfornon-compliancewithinanormaldistribution.
• Safeworkingloadasafunctionofmaterialgauge.• Useofappropriateloadspantablesasguides
tocladdingperformanceincorporatingbendingmoments.
• Potentialimpactsonperformanceandothercomponentsinthebuildingsystem.
2.0 Introduction
WhilstthethicknessofmetalselectedforusewillvarydependingonproductandapplicationthenominalvaluesinTable1aregenerallyacceptedasbeingnormallyusedintheUK.
Table 1
Millimetres (mm) Steel Aluminium
RoofWeatherSheet 0.7 0.8to1.2
WallWeatherSheet 0.5 0.8to1.2
Flashings 0.7 0.9
LinerSheet 0.4 0.5
StructuralLinerSheet 0.7 0.9
Whensheetmetalismanufacturedatthemillitisproducedtoatargetor‘nominal’thickness.However,aswithallmanufacturingprocessesitisinevitablethatthereisavariationintheproductionprocessand,assuch,variationsinthefinalthicknessofthefinishedmaterialisunavoidable.
3.1 SteelWithregardtotheselectionofsteelforuseinmetalroofingandcladdingapplicationsgaugetolerancesforhotdippedproductsaredeterminedfromthestandardBSEN10143:2006,Continuouslyhot-dipcoatedsteelsheetandstrip:tolerancesondimensionsandshape,andtheallowedpositiveornegativevariance(tolerance)comparedwiththenominalthicknessofthematerialvarieswiththenominalthickness,coilwidthandthegradeofsteel(asdeterminedbyitsminimumspecifiedyieldstrength).
UndernormalcircumstancesthesteelcoilusedinUKmarketsistypicallywithinthefollowingranges:-
• Nominalsteelthicknessesofbetween0.4mmand0.7mm.
• Coilwidthsof:-• lessthan1200mm• greaterthan1200mmandlessthanorequal
to1500mm• Minimumspecifiedyieldstrengthsof:-
• lessthan260MPa(260MN/mm2)
3.2 AluminiumThestandardfromwhichthetolerancesonthicknessofaluminiumsheetmaybedeterminedisasfollows:-
• BSEN485:Aluminiumandaluminiumalloys,sheet,stripandplate.Part4–tolerancesonshapeanddimensionsforcold-rolledproducts
ThetolerancespositiveornegativevaryaccordingtotheAlloyGroup(IorII)whichrelatetothechemicalcompositionofthematerialsandaredeterminedaccordingtoBSEN573:3.MaterialbelongingtoAlloyGroupIisnormallyusedforrollformingandconstructionpurposesintheUK.
4
3.0 Nominal thickness/gauge 4.0 Normal range of thickness
5
FromtheUKandEuropeanperspectivethekeyissueintermsofperformanceunderloadrelatestothebendingmomentofanyforceapplied.
Typically,theyieldstrengthofsteelsuppliedforthemanufactureofwallorroofprofilesisintherangelessthan260MPaandisgenerallyofyieldstrength220MPa.
Asoutlinedabove,aluminiumusedforrollformedproductsisinAlloyGroupIandusuallyfromseries3000and5000alloysforwhichthemaximumspecifiedmagnesiumandmanganesecontentsareeachnogreaterthan1.8%andtheirsumnogreaterthan2.3%.
Withreferencetothestandardsapplyingthetolerancesonthickness(inmillimetres)allowableforsteelmaterialswiththesetypicalcharacteristicsareasbelow:-
Theprofileofthefinishedproductwilltendtodictatetherequirementsofthemanufacturerwithregardtoselectionofthecoilwidthofthematerialinthefirstinstance.
Ingeneraltermsmostmanufacturersseektoachieveacoverwidthofthefinishedproductof1metrewithsteelroofingandwallingproducts.
• Weathersheetswithatypicalprofiledepthof31mmor32mmgenerateaneedforcoilwidthsoftheorderof1220mmto1250mm.
• Linersheetswithatypicalprofiledepthof19mmor20mmgenerateaneedforcoilwidthsoftheorderof1110mmto1150mm.
Aluminiumsheetproductsavailableinthemarkettypicallyprovidecoverwidthsofthefinishedproductofupto500mmandwouldassuchrequirecoilwidthofupto700mmalthoughcertainprofilescouldrequirecoilwidthsoflessthan500mm.
Itisworthyofnotethataluminiumprofilesmadefromcoilsofgreaterwidthareavailableinthemarket.
5.0 Commonly used coil widths
6.0 Yield strengths – construction purposes
Table 2
Nominal thickness
± Tolerance in mm for given width
Normal Tolerances Special Tolerances
Min Max ≤ 1200 1200 ≤ 1500 ≤ 1200 1200 ≤ 1500
0.2 0.4 0.040 0.050 0.030 0.035
0.4 0.6 0.040 0.050 0.035 0.040
0.6 0.8 0.050 0.060 0.040 0.045
0.8 1.0 0.060 0.070 0.045 0.050
1.0 1.2 0.070 0.080 0.050 0.060
AsummaryofthetolerancesonthicknessallowableforaluminiumfromAlloyGroupIarecontainedinthefollowingtable:-
Table 3
Specified Thickness ± Tolerance in mm for given width
Min Max ≤ 1000 1000 ≤ 1250 1250 ≤ 1600
0.2 0.4 0.020 0.040 0.050
0.4 0.5 0.030 0.040 0.050
0.5 0.6 0.030 0.050 0.060
0.6 0.8 0.030 0.060 0.070
0.8 1.0 0.040 0.060 0.080
1.0 1.2 0.040 0.070 0.090
1.2 1.5 0.050 0.090 0.100
Asmaybeseenfromtheforegoingkeypointswithregardtomaterialspecificationthereareseveralfactorstobeconsideredwhenselectingmaterial(s).
7.1 SteelIntermsofcoilwidthandyieldstrengththerangesforcompliancearerelativelywide.
Howeverintermsofthenominalthicknessofthemetalitisimportantthat:-
• Thematerialisspecifiedtotheappropriatetolerance.• Thematerialissuppliedasspecified.• Itisunderstoodwhatisbeingmeasuredandhow.
Inordertohighlightthepotentialfornon-complianceitissensibletoconsiderthecaseforeachnominalthicknessusedineverydaycircumstancesasfollows:-
7.1.1 Roofing weather sheetNormallytheoutersheetofaroofwillutiliseaprofilemanufacturedfromcoilof1250mmwidthwithnominalthicknessof0.7mmandminimumspecifiedyieldstrengthof220MPa.
FromBSEN10143:2006thetoleranceonthicknessis±0.06mm(seetablesinSection6.0)thelowerlimitonthicknessbeing0.64mmwithanupperlimitof0.76mm.
Ifweconsiderthat100%ofmaterialcanbeproducedwithinthesetolerancelimitsbytheproducingsteelmillitisreasonabletoassumethatthethicknessesmeasuredacrossawideenoughsamplewouldbenormallydistributed–i.e.followabellshapeddistributioncurveaboutthemid-pointoftherange
Figure 1
7.1.2 Walling weather sheetTheoutersheetofawallwilltypicallyutiliseaprofilemanufacturedfromcoilof1250mmwidthwithnominalthicknessof0.5mmandminimumspecifiedyieldstrengthof220MPa.
FromBSEN10143:2006thetoleranceonthicknessis±0.05mm(seetablesinSection6.0)thelowerlimitonthicknessbeing0.50mmwithanupperlimitof0.55mm.
6
7.0 Tolerance specification – potential for non-compliance
0.58 0.59 0.60 0.61 0.62 0.63 0.64 0.65 0.66 0.67 0.68 0.69 0.70 0.71 0.72 0.73 0.74 0.75 0.76 0.77 0.78Actual Thickness (millimetres)
0.64 0.675 0.70
Sheets that areoutside tolerance
Sheets that are within tolerance but may notnecessarily be regarded as 0.7mm nominal
0.7mm nominal to BSEN 10143:2006
0.7mm nominal to EN 10143:1993
0.675mm nominal to BSEN 10143:2006
0.64mm nominal to BSEN 10143:2006
0.675mm nominal to BSEN 10143:2006 half tolerance
7
Figure 2
0.40 0.41 0.42 0.43 0.44 0.45 0.46 0.47 0.48 0.49 0.50 0.51 0.52 0.53 0.54 0.55 0.56 0.57Actual Thickness (millimetres)
Sheets that areoutside tolerance
Sheets that are withintolerance but may not
necessarily be regardedas 0.55mm nominal
0.45 0.48 0.550.50
0.5mm nominal to BSEN 10143:2006
0.48mm nominal to BSEN 10143:2006
0.45mm nominal to BSEN 10143:2006
0.48mm nominal to BSEN 10143:2006 special tolerance
0.82 0.83 0.84 0.85 0.86 0.87 0.88 0.89 0.90 0.91 0.92 0.93 0.94 0.95 0.96Actual Thickness (millimetres)
Sheets that areoutside tolerance
Sheets that are withintolerance but may not
necessarily be regardedas 0.9mm nominal
0.86 0.88 0.90
0.9mm nominal to BSEN 485-4
0.88mm nominal to BSEN 485-4
0.86mm nominal to BSEN 485-4
0.88mm nominal to BSEN 485-4 half tolerance
7.2 Aluminium weather sheetMostaluminiumweathersheetswillbemanufacturedfrommaterialoflessthan1000mmwidthwithnominalthicknessof0.9mmandfromAlloyGroupI.
FromBSEN485-4thetoleranceonthicknessis±0.04mm(seetablesinSection6.0);thelowerlimitonthicknessbeing0.86mmwithanupperlimitof0.94mm
Figure 3
7.3 FlashingsFlashingsaretypicallymadefrommetalofnominalthicknessinaccordancewiththeroofingweathersheet,i.e.0.7mminthecaseofsteel.
Themostcommonlyidentifiedeffectcausedthroughthesupplyofbelowtolerancemetalforflashingsisthetendencyoftheflashingtoboworripplepostinstallation.
Generallywhilsttherearefewguaranteesorwarrantiesappliedinthecaseofflashingsandwhilsttheremaybenomajorstructuralimplicationresultingfromthesupplyofoutoftolerancematerialtheflashingshaveamajorrolewithregardto:-
• Weathertightnessofthecompletedbuilding.• Robustdetail–theinterfacesbetweenthestructuralelements.• Aestheticappearance.
Henceitisoftheutmostimportanceinthisregard,whetherrelatingtowateringressorairtightness,thatgreatattentionispaidtothespecificationofthematerialsusedforthemanufactureofflashingssincetheimpactismostnoticeableattheinterfacebetweencomplementarysystems.
7.4 Liner sheetsThelinersheetofarooforawallinabuiltupconstructionwilltypicallyutiliseaprofilemanufacturedfromcoilof1150mmwidthwithnominalthicknessof0.4mmandminimumspecifiedyieldstrengthof220MPa.
FromBSEN10143:2006thetoleranceonthicknessis±0.04mm(seetablesinSection6.0)thelowerlimitonthicknessbeing0.36mmwithanupperlimitof0.44mm.
Whilsttheforegoingrepresentswhatthestandardontoleranceforsteelwithnominal0.4mmthicknessallows,itshouldbenotedthattoensurefullcomplianceandsaferoofingsystems,MCRMAmembershaveundertakentoonlyprovidelinersheetwithactualthicknessof0.4mmorgreater.
Figure 4
Asmaybeseenfromthegraphicsitispossibletospecifyanominalthickness(thatwhilstnotnecessarilytheacceptednominalthicknessforthatparticularuse)withatolerancethatcouldbecontainedwithinthetolerancesforthenominalthicknesswhetherunderBSEN10143:2006orBSEN485-4;i.e.byspecifyinga(target)thicknesswithspecialtolerance,forexample‘halftolerance’or‘zeronegative/fullpositive’tolerance.
Itisnotpossibletospecifyalowerthannominalthicknessundernormaltolerancesandbeabletoguaranteethatthecoilwillbewithintoleranceforagenerallyacceptednominalthicknessforthatparticularuse.Thismeansthatonsomeoccasionsthecoil(duetothenormaldistributionofmanufacturingprocesses)willbebelowthelowestlevelofthicknessallowableandhenceoutoftolerance.
8
0.32 0.33 0.34 0.35 0.36 0.37 0.38 0.39 0.40 0.41 0.42 0.43 0.44 0.45 0.46Actual Thickness (millimetres)
Sheets that areoutside tolerance
Sheets that are withintolerance but may not
necessarily be regardedas 0.4mm nominal
0.36 0.38 0.40
0.4mm nominal to BSEN 10143:2006
0.38mm nominal to BSEN 10143:2006
0.36mm nominal to BSEN 10143:2006
0.38mm nominal to BSEN 10143:2006 half tolerance
9
Coatedmetalsmayhaveaprotectivecoatinganddecorativefinishtobothsides;eachofthesecoatingshasitsowntolerance.
HowtheselayersofsurfacetreatmentsandcoatingscombinetoproducethefinishedproductisshowninFigure5below.
Figure 5
AccordingtoBSEN10143:2006thethicknessofsteelsubstrateshouldbemeasuredaminimumdistanceof40mmfromthecutedge;foraluminiumunderBSEN485-4thisdistanceis10mm.
IntheUKthemostcommonlyusedexternalcoatingforsteelisplastisolof200micronsthicknesswithanembossedfinishaccompaniedbyareversesidecoatingofupto20microns,dependingontheapplication,butotherfinishesdoexistandeachhasitsown‘normal’thicknessandtolerance.Otherpaintfinishesorcoatingsmaybeappliedwhetherpolyesterorsimilarwithvaryingthicknesses,eachwiththeirowntolerancelevels.
Similarlyaluminiummayalsobesuppliedwithapaintcoating.ForexternalpurposesthemostcommonlyusedwouldbeaPVDFmaterialof25micronthicknessandforinternalpurposesof15or18micronthickness.
Manyaluminiumapplicationsretainthestandardmillfinishandforflashingsandsimilarapplyapowdercoatingtreatmentpostmanufacture.
Allcoatingsappliedaredesignedtoprovideaparticularcharacteristicintermsofthepaintsystembutdonotcontributedirectlytotheloadbearingcapabilityofthemetal.
Itisimportantinmeasuringgaugetoonlymeasurethoseelementswhichbeartheload.Thisisnecessarysinceeachcoatingthatisappliedcarriesatoleranceonthicknessandwhilstitmayappearsimplertomeasuretheexternalthicknessofthewholepaintsystemitcannotberelieduponasatrue(orindicative)measureofthethicknessofthesubstrateanditsmetalliccoating.
Forexample,inthecaseofacompletepaintsystemofupto0.25mmthickness,tolerancesofsayapproximately0.03mmarepossiblewhich,inthecaseofthesebeingpositivewherethesteelsubstratewasbelowthelowertolerancelimit,couldresultinatotalthicknessappearingtobeacceptablewithinthe“overall”measureofthickness.
Thereforeinordertoproperlymeasurethetruethicknessoftheloadbearingelementitisnecessarytoremovethepaintcoatings.Thismaysimplybeachievedthroughtheappropriateuseofaproprietarypaintstripper,takingcaretofollowtheguidanceonuse.
Thismeasurementshouldbeconductedbyuseofaproperlycalibratedmicrometerasshown…
8.0 Measuring the thickness of a coil or sheet
α α
TopcoatPrimer
Pre-treatmentMetalliccoating
SubstrateMetalliccoating
Pre-treatmentBackingcoat
10
Intuitivelyitisstraightforwardtounderstandthatasthethicknessofagivenmaterialreducessodoesitsresistancetobendingunderloadingconditions,assumingthatallothercharacteristicsofthematerialremainconstant,i.e.composition,yieldstrengthandcoilwidth.
Figure 6
Figure6showstherangeofvariationtypicallyoccurringwherespanconditionsaredifferentforthesamematerial,wherethethicknessistheactualmaterialgaugeafterallowingforcoatingsystems.
However,itshouldalsobenotedthatformaterialswhich,insomecases,maypossiblybeconsideredtobewithintolerancebutnotnecessarilycomplyingwithanominal0.7mmthickness,thesafeworkingloadcapabilitymaybereducedbyfactorsinexcessof20%,i.e.wheretheactualthicknessis0.58mmorless(seeFigure2).
TheinformationusedtoconstructtheabovegraphsistakenfromtheloadspantablesofMCRMAmembersusingCorusColorsmaterialandverifiedtoEC3methods.*
*Note: These calculations were produced for Corus Colours by the Steel Construction Institute. The profile was a typical 32/1000 which could be manufactured from one or all of Corus’s supply chain partners. The properties were calculated to EC3 using material with a minimum yield strength and using material with tolerance as defined within EN 10143:2006
TheCEmarkanditsassociatedinformationlabelhelpsdemonstratethatanyproducthasbeentestedinaccordancewiththeappropriateEuropeanstandardandinthecaseofmetalsuppliedforwallingandroofingapplicationscomplieswiththeConstructionProductsDirective.
WhereCEmarkingisinplacetheproductshouldbesuppliedwithlabelsorpackagingthatclearlyidentifythevaluesofthecharacteristicstested,allofwhicharesubjecttoexternalinspectionandchecking.
TherequirementforCEmarkingofcoilorsheetwillrequirethefollowingtobeincludedinthelabelling:-
• Standardtowhichtheproducthasbeenmanufactured
• Toleranceclass• Descriptionoftheproduct
• Coilwidth• Yieldstrength• Coatings,paintfinish(es),andcolour
• Firerating
Itshouldbenotedthatwithinthetolerancesallowedtherearethreeclassifications,asfollows:-
• Class1 Full(normal)tolerance
• Class2 Specialtolerance
• Class3 Zeronegativetolerance
Theproductspecificationandrequirementsforsupplyof‘Selfsupportingmetalsheetforroofing,externalcladdingandinternallining’arecoveredinBSEN14782:2006,whichagainallowsforthecomparisonbetweenproductssuppliedandcoverthefollowingcriteria:-
• Nominalgauge• Resistanceofroofingproductstoconcentrated
forces• Externalfireperformance• Reactiontofireperformance
9.0 CE Marking – ensuring that the correct material is delivered
10.0 Safe working load as a function of material thickness
0.58 0.60 0.62 0.64 0.66 0.68 0.70 0.72Thickness (mm)
Single spanDouble spanMulti span
Load (kN/m2)
Safe Working Load at 1.8m span for given thickness on 32/1000 profile
2.3
2.1
1.9
1.7
1.5
1.3
1.1
0.9
}
Reduction in SWLacross bottomtolerance for 0.7mmnominal thickness
11
withstandtheloadsproducedbythosepersonsconductinganysuchwork.
Thedesignloadstobemetare:-
• Generalloadof0.6kN/m2
• Pointloadof0.9kN
TheseperformancecriteriaareestablishedinaccordancewithEC3.
Anyfailuretomeetthenominalrequirementswithintherelevantstandardsmayaffectthecapabilityofthesystemorproducttomeettherequiredloadspanrequirementsandincreasethepotentialforfailure.
11.3 Use of load span tablesEachmanufacturer/supplierofprofiledmetalsheetusedforconstructionwillprovideasamatterofcourseasetofloadspantableswhichservetoassistintheselectionoftheappropriatemetalcladdingorroofingsolutionforagivensetofdesignparametersorlikelyloadingconditionsinuse.
Whatwillbenoticedisthateachmanufacturerwillidentifyslightlyvaryingfigureseitherforspan,givenasetload,orforthemaximumsafeimposedloadgivenaspecificspanrequirement.
Itisimportanttobeawareofthesedifferencessincetheyariseforavarietyofreasonsbutmaynormallybeattributedtothefollowing:-
• Choiceofmaterial• Profiledesign/shape• Fixingregime
Thechoiceofmaterial,themainsubjectofthispaperwilltosomedegreeimpactontheothertwopotentialvariants.
11.1 Non fragilityAmajorcauseforconcerninconstructionworkisthepotentialfordeathorseriousinjurycausedbyfallsfromheightandinparticularfrom,orthrough,aroof.
Itisclearlynecessarytoensurethatallworkingconditions,safesystemsofworkandmaterialsspecifiedshouldtakeaccountofthispotential.
Itisappropriatethatthefollowingpointsshouldbeaddressedinthespecification:-
• Thespecifiedconstruction/assemblyisdesignatedasbeingnon-fragile.
• Thesupplierclassifiestheroofsystemasbeingnon-fragileandcansupportthisclaimwithrelevanttestdata.
• Anyconditionaffectingthenon-fragilityoftheconstructionshouldbeclearlystated.
CompliancewiththesekeypointswillhelpensureadherencetotheACR(CP)001:2007Rev3Recommended Practice for Work on Profiled Sheet Roofs.
Howtocheckwhetheraparticularroofsystemmaybeconsiderednon-fragileiscoveredinACR(M)001:2005Test for Non-Fragility of Profiled Sheet Roof Assemblieswhichverifieswhetherthesystemcansupportwithoutcatastrophicfailuretheloadsthatwillbeappliedbyapersonfallingontoit.
11.2 WalkabilityWalkabilityisacommonlyusedword/phrasewhichtendstobeusedforthickerlinersheetsystemsbutwhichshouldnotnecessarilybeusedtodenotemetalthicknesssincethephrasemayonlybeconsideredappropriatewherethesystemiscompletelyfixedanddeemednon-fragile.
Theneedforawalkablelinersometimesarisesfromthedesiretousealinersystemasasafemethodofaccessbutwithoutthepotentialfordamagethroughlocaldistortiontothesheet.
Thelikelihoodofdeformationordamagetoanysheetthatiswalkeduponisincreasedwiththinnermaterials.Productsthathaveshallowerprofilesaremorelikelytobesusceptibletodamageordistortion.
Wheresafeaccesstoaroofforgeneralmaintenanceandrepairsarerequired,themetalsystemmustbedesignedtoaccommodateand
11.0 Resistance to loading
Aswithallrooforwallsheetingthedesignoftheprofilewillhelpdetermineitsloadbearingcapabilityinuse;allprofileswillhavetheirownvariationsdependingon:-
• Historicperspective• Rollformingequipmentused
Thedimensionsofthesheet,forexampleinatypical32/1000roofingprofilemadefromsteelwithanominal0.7mmsteelwillvaryacrosseachelementtoachievethe1000mmcoverwidthrequirement.
Variationsinthefollowingelementswillhelpdeterminehowtheprofileperformsinuse:-
• Profilepitch• Profiledepth• Crownwidth• Valleywidth• Ribwidth• Web
Figure7belowidentifieswhereeachofthesedimensionsaremeasuredandhelpsdemonstratehowtheadjustmentofoneparticulardimension(orangleoftherib/web)willaffecttheotherdimensionswithinanygivenwidthofcoil.
Figure 7
Forgreaterloadbearingcapabilitiesprofilesmaybedesignedwithadditionalstiffeningribsagain,theplacementandsizeoftheseribswillvaryfromonemanufacturertoanother.
Itshouldbenotedthateachmanufacturerpublishesitsloadspantablesbaseduponthemanufactureofitsprofileswithmaterialofnominalthickness.
Whereanydoubtexistswithregardtosafeloadbearingcapabilityforanyparticulardesignthenadviceshouldbesoughtfromthemanufactureroraqualifieddesignengineer.
Clearlywhereprofilesarepotentiallymanufacturedfrommetalthatisincorrectlyspecifiedwithregard
12
toitsthicknessandhasthepotentialtobeoutoftolerancethentheloadspantablesarenotapplicableandappropriateexpertadviceshouldbetaken.
12.0 Profile shape
Profile pitchRib widthValley width
Web
Profiledepth
Cover widthCrown width
13
Thefireperformanceofroofingandwallingsystemsareconsideredseparately.
14.1 Roofing applicationsThegenericperformanceofsteelandaluminiumsystemsinroofingapplicationshasbeenassessedaccordingtoEN1187andallocatedasfollowsunderrelevantCommissionDecisionsrelatedtothecalorificvalueofthematerialassummarisedbelow:-
Table 4
CommissionDecision
CoatingCalorificValue
Classification Notes
2000/553/EC <4MJ/m2 Satisfieswithouttheneedfortesting
2005/403/EC <8MJ/m2BROOF(1);BROOF(2),BROOF(3)
MaxDryMassof330g/m2
Bothoftheabovedecisionshaveaspecificrequirementthatthethicknessofthematerialbegreaterthan0.4mm.
14.2 Walling applicationsAswithloadbearingcapabilityitisperhapsintuitivethatmaterialthicknesshasaneffectonthefireperformanceofpre-finishedsteelinwallingapplicationswithregardtoreactiontofire;thisissupportedbyresearchthroughtheEuropeantechnicalcommittees.
Thereactiontofireperformancewhichisnormallyquotedisforsteelwhichhasgreaterthicknessthanthematerialwhichwastested.
Moststeelsheetingforwallcladdingis0.5mmorgreater.Fortheclassificationtobevalidthetestingmusthavebeenconductedonmaterialofatleast0.5mm.
WherethematerialdoesnotmeettherequirementsofBSEN10143:2006itmaynotclaimtheclassification.
Warrantiesorguaranteesofperformancereceivedfrommanufacturersaregenerallyexplicitwithregardtotheneedforfixinginaccordancewiththeirownspecificmethods,typeoffixing,frequency,maximumspacingandsoon.
Thesefixingrequirementsaremadebasedupontheuseofnominalthicknessmaterial.
Theuseofmaterialsthatarethinnerthanthetolerancelimitswilltendtoripple(seesection7.3onflashings)anddeliverimpairedperformanceregardlessofwhethertheappropriatefixingregimehasbeenapplied.
Aswithallfixingsitisnecessarythatthecorrectfastenerisusedwithregardtotheapplicationandthatthefastenersarefixedwiththecorrecttorquesetting–anyover-tighteningwilltendtocausedistortionaroundthefastenerandthiswillbecomeemphasisedwherelightergaugematerialisused.
Thepotentialforfailureinfastenersishighlightedinareasofmaximumloadingwherethinner/lightergaugematerialsareused.Importantissuestobeawareofinthesecircumstancesmaybesummarisedas:-
• Potentialforfastenerstearingorpullingthroughlightergaugecladdingsheet.
• Theneedfortorquecontrolwhenfixingtoavoidthreadstripping.
• Localdistortionwhichmayleadtopoolingonroofsandincreasedpotentialforcorrosionandfailure.
14.0 Fire performance13.0 Fixing regime
OtherMCRMAdocumentsdealmorespecificallywithissuesrelatingtointeractionsbetweenvariouscomponentswithinanybuildingsystembutitisworthyofnoteinthiscontextthatwherenominalthicknessandthepotentialtobeoutoftoleranceisapossibilitythenfurtherimpactswillneedtobeconsidered.
Fromamaterialselectionpointofviewthispaperhasidentifiedthereductioninsafeworkingloadforagivenspanasbeingsignificantasmaterialthicknessreduces.
Reductionsinsafeworkingloadofcirca20%will,towardsthelimitsofloading,compromisethestructure.
Whatshouldalsobeborneinmindisthatunderthecontinuousstressesandstrainsofnormallifeabuildinganditsenvelope(wallorroof)issubjecttoloadandre-loadovertime,whetherpositive(gravity)ornegative(suction).Itissensibletoconsiderthatwhereamaterialisbelowitstolerancelimitthenitislessabletosustaintherigoursofconstantchange.
Itisconceivablethatsuchchangesaremostlikelytoberecognisedearly(ifnotthroughcatastrophicfailure)atthosepointswherethecumulativeeffectsofanytolerancevariationaremagnified,i.e.atfixedpoints.
Inthecaseofcladdingorroofingthiswillbewherethesystemisfixedeitherbypurlinorothersupportstructuretothemainstructureandthroughthefixings.
14
Thefactthatmanufacturersrequiretolerancesagainstwhichtheymanufacturedemonstratesthatwithinanyprocessthereisthepotentialforarangeofoutcomesregardlessofthecontrolexertedduringtheprocess.
Inordertoensurethattheappropriatelevelsofsafetyaremetandadheredto,itisimperativethatinthespecification,manufactureanduseofmetalinwallingandroofingapplicationsallduecareistakenandthatthematerialssuppliedandusedarewithinthetolerancesallowedbytherelevantstandardswhetherforsteeloraluminium.
Itispossibletospecifymaterialsandspecialtolerancesthatarenotnecessarilyaddressedwithinthestandardsbutthatthesemustbecapableofbeingachievedbythemanufacturerandagreedbetweentheparties–itthenbecomestheresponsibilityofthemanufacturer/supplier(mill)tomeettheagreedspecification.
Thepotentialforadverseimpactwithregardtosafeworkingloadissignificantinthecaseofmaterialssuppliedandusedbelowtheminimumtolerancesallowed;theimportanceofappropriateprofessionaladviceonthevalidityofloadspantablesandspecificloadingconditionscannotbeoverstated.
TheMCRMA,itsmembersandassociatesremaincommittedatalltimestothecontinuingdevelopmentandsafeuseofmetalcladdingandwallingsystems.
16.0 Conclusions15.0 Interaction with other building components
15
BSEN10143:2006–Continuouslyhot-dipcoatedsteelsheetandstrip:Tolerancesondimensionsandshape
BSEN485:Aluminiumandaluminiumalloys,sheet,stripandplate.Part4:Tolerancesonshapeanddimensionsforcold-rolledproducts
BSEN573:3
BSEN14782:2006Selfsupportingmetalsheetforroofing,externalcladdingandinternallining.Productspecificationandrequirements
EC3–Eurocode3:Designofsteelstructures(EN1993)
ACR(CP)001:2007:Recommendedpracticeforworkonprofiledsheetroofs.
ACR(M)001:2005:TestforNon-Fragilityofprofiledsheetroofassemblies
EN1187:2002:Testmethodsforexternalfireexposuretoroofs
2000/553/EC:Externalfireperformanceofroofcoverings
2005/403/EC:Externalfireperformanceofroofsandroofcoverings
PermissiontoreproduceextractsfromtheBSstandardsreferredtointhisdocumentisgrantedbyBSI.BritishStandardscanbeobtainedinPDForhardcopyformatsfromtheBSIonlineshop:www.bsigroup.com/ShoporbycontactingBSICustomerServicesforhardcopiesonly:Tel:+44(0)2089969001,Email:[email protected].
17.0 Bibliography
16
MCRMA technical papers
No1 Recommendedgoodpracticefordaylightinginmetalcladbuildings
No2 Curvedsheetingmanual
No3 Secretfixroofingdesignguide
No4 Fireandexternalsteel-cladwalls:guidancenotestotherevisedBuildingRegulations,1992(out of print)
No5 Metalwallsystemsdesignguide
No6 Profiledmetalroofingdesignguide
No7 Firedesignofsteel-cladexternalwallsforbuilding:construction,performancestandardsanddesign
No8 Acousticdesignguideformetalroofandwallcladding
No9 Compositeroofandwallcladdingpaneldesignguide
No10Profiledmetalcladdingforroofandwalls:guidancenotesonrevisedBuildingRegulations1995partsL&F(out of print)
No11Flashingsformetalroofandwalls:design,detailingandinstallationguide
No12Fastenersformetalroofandwallcladding:designdetailingandinstallationguide
No13Compositeslabsandbeamsusingsteeldecking:bestpracticefordesignandconstruction
No14GuidanceforthedesignofmetalroofingandcladdingtocomplywithApprovedDocumentL2:2001
No15NewApplications:compositeconstruction
No16Guidancefortheeffectivesealingofendlapdetailsinmetalroofingconstructions
No17DesignguideformetalroofingandcladdingtocomplywithenergyrequirementsofUKBuildingRegulations(2006)
No18ConventionsforcalculatingUvalues,f-valuesand-valuesformetalcladdingsystemsusingtwo-andthree-dimensionalthermalcalculations
No19AdynamicthermalmodellingstudyofatypicalmetalcladdingbuildingtoevaluateoverheatingintheUnitedKingdom
Pleasenote:PublicationscanbedownloadedfromtheMCRMAwebsiteatwww.mcrma.co.uk
LiabilityWhilst the information contained in this design guide is believed to be correct at the time of going to press, the Metal Cladding and Roofing Manufacturers Association Limited and its member companies cannot be held responsible for any errors or inaccuracies and, in particular, the specification for any application must be checked with the individual manufacturer concerned for a given installation. The diagrams of typical constructions in this publication are illustrative only.
Metal Cladding & Roofing Manufacturers Association Ltd106 Ruskin Avenue Rogerstone Newport South Wales NP10 0BD01633 895633 | [email protected] | www.mcrma.co.ukde
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