Reliabilitydifferentiation The degree of reliability shouldbe adopted to suit the use of thestructure,the type of structure or structural element and thesituation considered inthe design, etcFor the purpose of reliability differentiation,consequencesclasses (cC) maybeestablishedbyconsideringtheconsequencesoffailure ormalfunctionofthestructureDescriptionExamples of buildings andcivil engineering worksCC3SeriousconsequencesGrandstands,publicbuildingswhereconsequencesoffailure are high (e.g.a concert hall)CC2ModerateconsequencesResidentialandofficebuildings,publicbuildingswhereconsequencesoffailureare medium (e.g.anofficebuilding)CC3LowconsequencesAgriculturalbuildingswherepeopledonotnormallyenter(e.g.storagebuildings),greenhouses1Ref: 4, 5
Reliability differentiation 11 The degree of reliability should be adopted to suit the use of the structure, the type of structure or structural element and the situation considered in the design, etc For the purpose of reliability differentiation, consequences classes (CC) may be established by considering the consequences of failure or malfunction of the structure Description Examples of buildings and civil engineering works CC3 Serious consequences Grandstands, public buildings where consequences of failure are high (e.g. a concert hall) CC2 Moderate consequences Residential and office buildings, public buildings where consequences of failure are medium (e.g. an office building) CC3 Low consequences Agricultural buildings where people do not normally enter (e.g. storage buildings), greenhouses Ref: 4, 5
Reliabilitydifferentiation..TargetReliabilitiesThereliabilityclasses(RC)maybedefinedbytheβreliabilityindexconceptThreereliabilityclassesRC1,RC2andRC3maybeassociatedwiththethreeconsequencesclassesCC1,CC2andCC3ReliabilityMinimumvaluesforβClass1year reference50years referenceperiodperiodRC35.2 (Pf ~ 9.9e-8)4.3 (Pf ~8.5e-6)RC24.7 (Pf~1.3e-6)3.8 (Pf ~ 7.2e-5)RC14.2 (Pf ~ 1.3e-5)3.3 (Pf ~ 5x×10-4)12Ref: 4, 5
Reliability differentiation . . . 12 Target Reliabilities The reliability classes (RC) may be defined by the β reliability index concept Three reliability classes RC1, RC2 and RC3 may be associated with the three consequences classes CC1, CC2 and CC3 Reliability Class Minimum values for β 1 year reference period 50 years reference period RC3 5.2 (Pf ≈ 9.9e-8) 4.3 (Pf ≈ 8.5e-6) RC2 4.7 (Pf ≈ 1.3e-6) 3.8 (Pf ≈ 7.2e-5) RC1 4.2 (Pf ≈ 1.3e-5) 3.3 (Pf ≈ 510-4 ) Ref: 4, 5
Principlesof limitstatedesignEurocodesadoptthepartialfactorsmethod,orlimitstatessemi-probabilistic method,as themethod forthe verification of structuralsafetyDesignfor limitstates shall be basedonthe useof structuraland loadmodelsforrelevantlimitstatesIt shall beverifiedthatnolimit stateisexceeded whenrelevantdesignvaluesforactions,material andproduct propertiesandgeometricaldataareusedinthesemodels Theultimate limit statesareassociated withloss of equilibriumof thewholestructure,orfailureorexcessivedeformationofastructuralmemberandtheygenerallyconcernsafetyofpeopleFortheverificationofultimatelimit statedesignactionsshall not exceedthedesignresistanceofthestructuralelementQd≤Rd13?Ref: 4,5
Principles of limit state design 13 Eurocodes adopt the partial factors method, or limit states semiprobabilistic method, as the method for the verification of structural safety Design for limit states shall be based on the use of structural and load models for relevant limit states It shall be verified that no limit state is exceeded when relevant design values for actions, material and product properties and geometrical data are used in these models The ultimate limit states are associated with loss of equilibrium of the whole structure, or failure or excessive deformation of a structural member and they generally concern safety of people For the verification of ultimate limit state design actions shall not exceed the design resistance of the structural element Qd ≤ Rd Ref: 4, 5
Principlesof limit statedesign.Serviceabilitylimitstatescorrespondtoconditionsbeyondwhichspecified servicerequirementsfora structure or structuralmemberarenolongermetExceedingtheselimitscauseslimiteddamagebutmeansthatthestructuresdo notmeetdesignrequirements,functionalrequirements,comfort of users,appearance etcEN199oindicatesthreedifferenttypesof combinationsforserviceability limit states verifications:characteristic combinationfrequentcombinationandquasi-permanentcombinationUsually the serviceabilityrequirements areagreed for eachindividual project14Ref: 4, 5
Principles of limit state design . . . 14 Serviceability limit states correspond to conditions beyond which specified service requirements for a structure or structural member are no longer met Exceeding these limits causes limited damage but means that the structures do not meet design requirements, functional requirements, comfort of users, appearance etc EN1990 indicates three different types of combinations for serviceability limit states verifications: characteristic combination frequent combination and quasi-permanent combination Usually the serviceability requirements are agreed for each individual project Ref: 4, 5