SummaryofBS476:Part20:1987Methodfordeterminationofthefireresistanceelementsofc***truction(generalprinciple)PurposeTheobjectiveofdeterminingfireresistance,asdescribedinthisPartandtheassociatedPartsofBS476,istoassessthebeh***iourofaspecimenofanelementofbuildingc***tructionwhensubjectedtodefinedheatingandpressureconditi***.Themethodprovidesameansofquantifyingtheabilityofanelementtowithstandexposuretohightemperatures,bysettingcriteriabywhichtheloadbearingcapacity,thefirecontainment(integrity)andthethermaltran***ittance(insulation)functi***canbeadjudges.BS476:Part20providesguidanceonthegeneralprinciplesofthetestmethodforfireresistanceandshouldbeusedinconjunctionwithBS476:Part21to23.TestspecimenThetestspecimenandanyassociatedc***tructionformingatestc***tructionareidenticalto,orrepresentativeof,theelementofbuildingc***tructionthatistobeevaluated.Fornon-separatingelements,separatingelementsthatareonlyrequiredtoresistfirefromonesideinuse,andforverticalsymmetricalseparatingelements,onlyonespecimenistested.Forverticalasymmetricalseparatingelementsthatarerequiredtoresistsfirefromeitherside,theelementistestedfromeachsideusingaseparatespecimen.Whereverpossible,testspecimensarefull-sizedelementsofbuildingc***tructionandunlessitisimpossible,theindividualcomponentsmakingupatestspecimenarealsofull-sized.Wheretheaboveisnotpossible,theminimumsizeoftheelementsshallbe:Non-separatingelements:Vertical:3mhighHorizontal:4mhighSeparatingelements:Vertical:3mhighby3mwideHorizontal:4mspanby3mwideFornon-loadbearingelements,thetestc***tructionismountedasinpractice.Forloadbearingelements,thetestloadingisselectedtorepresenttheconditionapplicabletotheelementinpractice.ApparatusThisc***istsessentiallyof:1.Afurnaceofadesignappropriatetothetypeofspecimenbeingtestedtoallow:a.verticalseparatingelementstobeexposedtotheheatingandpressureconditi***ononeface.b.Horizontalseparatingelementstobeexposedtoheatingandpressureconditi***fromtheundersides.c.Beamsnormallytobeexposedtotheheatingandpressureconditi***onthreefaces,i.e.thesoffitandtwosides,butprovisionshouldbemadetoenablebeamstobetestedwithallfourfacesexposed.d.Freestandingcolumnstobeexposedtotheheatingandpressureconditi***equallyonallfourfaces.ThefurnaceisfuelledbyeithernaturalgasorLPGasandhasthermocoupleslinkedtoassociatedtemperaturemeasuringdevicesfordeterminingthetemperatureatspecificpositi***.Apressuresensingprobeisalsositedwithinthefurnace.2.Loadingequipment.Atestloadingisappliedtothespecimeneitherbydeadweightsorbyahydraulicormechanicaljackingsystem,orbyacombinationofboth.3.Specimensupportsystemstoapplyrestraintattheedgesorendsofthespecimen.4.Monitoringequipmentc***istingiffixedspecimensurfacethermocouples,arovingsurfacethermocouple,acottonpadformonitoringpermeability,gapgaugesformonitoringimpermeability,deformationmeasuringdevicesandaradiometer.MethodArepresentativesampleoftheelementisexposedtoaspecifiedregimeofheatingunderpositvepressureandtheperformanceofthetestsampleismonitoredonthebasisofcriteriadescribedintheStandard.Fireresistanceofthetestelementisexpressedasthetimeforwhichtheappropriatecriteriah***ebeensatisfied.Thetimessoobtainedareameasureoftheadequacyofthec***tructioninafirebuth***enodirectrelati***hipwiththedurationofarealfire.PerformancecriteriaThefireresistanceofthetestc***tructionisassessedagainstoneormoreofthecriteriaforloadbearingcapacity,integrityandinsulation,whicheverarerelevanttotheelementsusedinpractice.1.Loadbearingcapacity–failureisdeemedtoh***eoccurredwhenthespecimenfailstosupportthetestloading.2.Integrity–failureisdeemtooccurwhencollapseorsustainedflamingontheunexposedfaceoccurs,orthecriteriagivenforimpermeabilityareexceeded.3.Impermeability–failurehasoccurredwhenflamesandorhotgasescauseflamingorglowingofacottonpad,ora6mmdiametergapisformedwithalengthgreaterthan150mmora25mmdiametergapisformed.4.Insulation–failurehasoccurredif:a.themeanunexposedfacetemperatureincreasebymorethan140°Caboveitsinitialvalue,orb.thetemperaturerecordedatanypositionontheunexposedfaceismorethan180°Cabovetheinitialmeantemperature.Thestandardizedtemperature/timeconditi***usedIthisevaluationarerepresentativeofonlyonepossiblefireexposureconditionatthefullydevelopedfirestageandthemethoddoesnotquantifythebeh***iourofanelement,forapreciseperiodoftime,inarealfiresituation.Inaddition,duetorestricti***ofsizeandtheabsenceofsurroundingc***truction,thelaboratorytestcannotreproducetheactualbeh***iourpatternofanelementinafire.However,testdatacanprovideabasisformakingengineeringevaluati***.)