Factor of safety and probability安全系数与概率

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1、FactorofsafetyandprobabilityoffailureIntroductionHowdoesoneassesstheacceptabilityofanengineeringdesign?RelyingonjudgementalonecanleadtooneofthetwoextremesillustratedinFigure1.Thefirstcaseiseconomicallyunacceptablewhiletheexampleillustratedinthedrawing

2、ontherightviolatesallnormalsafetystandards.Figure1:Rockboltingalternativesinvolvingindividualjudgement.(DrawingsbasedonacartooninabrochureonrockfallspublishedbytheDepartmentofMinesofWesternAustralia.)SensitivitystudiesTheclassicalapproachusedindesigni

3、ngengineeringstructuresistoconsidertherelationshipbetweenthecapacityC(strengthorresistingforce)oftheelementandthedemandD(stressordisturbingforce).TheFactorofSafetyofthestructureisdefinedasF=C/DandfailureisassumedtooccurwhenFislessthanunity.Factorofsaf

4、etyandprobabilityoffailureRatherthanbaseanengineeringdesigndecisiononasinglecalculatedfactorofsafety,anapproachwhichisfrequentlyusedtogiveamorerationalassessmentoftherisksassociatedwithaparticulardesignistocarryoutasensitivitystudy.Thisinvolvesaseries

5、ofcalculationsinwhicheachsignificantparameterisvariedsystematicallyoveritsmaximumcrediblerangeinordertodetermineitsinfluenceuponthefactorofsafety.ThisapproachwasusedintheanalysisoftheSauMauPingslopeinHongKong,describedindetailinanotherchapteroftheseno

6、tes.Itprovidedausefulmeansofexploringarangeofpossibilitiesandreachingpracticaldecisionsonsomedifficultproblems.Onthefollowingpagesthisideaofsensitivitystudieswillbeextendedtotheuseofprobabilitytheoryanditwillbeshownthat,evenwithverylimitedfielddata,pr

7、actical,usefulinformationcanbeobtainedfromananalysisofprobabilityoffailure.AnintroductiontoprobabilitytheoryAcompletediscussiononprobabilitytheoryexceedsthescopeofthesenotesandthetechniquesdiscussedonthefollowingpagesareintendedtointroducethereadertot

8、hesubjectandtogiveanindicationofthepowerofthesetechniquesinengineeringdecisionmaking.AmoredetailedtreatmentofthissubjectwillbefoundinabookbyHarr(1987)entitled‘Reliability-baseddesignincivilengineering’.Apaperongeotechnicalapplicationsofprobabi