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附录：中英文翻译英文部分：LOADSLoadsthatactonstructuresareusuallyclassifiedasdeadloadsorliveloads.Deadloadsarefixedinlocationandconstantinmagnitudethroughoutthelifeofthestructure.Usuallytheself-weightofastructureisthemostimportantpartofthestructureandtheunitweightofthematerial.Concretedensityvariesfromabout90to120pcf(14to19KN/m)forlightweightconcrete,andisabout145pcf(23KN/m)fornormalconcrete.Incalculatingthedeadloadofstructuralconcrete,usuallya5pcf(1KN/m)incrementisincludedwiththeweightoftheconcretetoaccountforthepresenceofthereinforcement.Liveloadsareloadssuchasoccupancy,snow,wind,ortrafficloads,orseismicforces.Theymaybeeitherfullyorpartiallyinplace,ornotpresentatall.Theymayalsochangeinlocation.Althoughtitistheresponsibilityoftheengineertocalculatedeadloads,liveloadsareusuallyspecifiedbylocal,regional,ornationalcodesandspecifications.TypicalsourcesarethepublicationsoftheAmericanNationalStandardsInstitute,theAmericanAssociationofStateHighwayandTransportationOfficialsand,forwindloads,therecommendationsoftheASCETaskCommitteeonWindForces.Specifiedlivetheloadsusuallyincludesomeallowanceforoverload,andmayincludemeasuressuchaspostingofmaximumloadswillnotbeexceeded.Itisofternimportanttodistinguishbetweenthespecifiedload,andwhatistermedthecharacteristicload,thatis,theloadthatactuallyisineffectundernormalconditionsofservice,whichmaybesignificantlyless.Inestimatingthelong-termdeflectionofastructure,forexample,itisthecharacteristicloadthatisimportant,notthespecifiedload.Thesumofthecalculateddeadloadandthespecifiedliveloadiscalledtheserviceload,becausethisisthemaximumloadwhichmayreasonablybeexpectedtoactduringtheserviceresistingisamultipleoftheserviceload.StrengthThestrengthofastructuredependsonthestrengthofthematerialsfromwhichitismade.Minimummaterialstrengthsarespecifiedincertainstandardizedways.Thepropertiesofconcreteanditscomponents,themethodsofmixing,placing,andcuringtoobtaintherequiredquality,andthemethodsfor222testing,arespecifiedbytheAmericanConcreteInsititue(ACI).IncludedbyrefrenceinthesamedocumentarestandardsoftheAmericanSocietyforTestingMaterials(ASTM)pertainingtoreinforcingandprestressingsteelsandconcrete.Strengthalsodependsonthecarewithwhichthestructureisbuilt.Membersizesmaydifferfromspecifieddimensions,reinforcementmaybeoutofposition,orpoorplacementofconcretemayresultinvoids.Animportantpartofthejoboftheergineeristoprovidepropersupervisionofconstruction.Slightingofthisresponsibilityhashaddisastrousconsequencesinmorethanoneinstance.StructuralSafetySafetyrequiresthatthestrengthofastructurebeadequateforallloadsthatmayconceivablyactonit.Ifstrengthcouldbepredictedaccuratelyandifloadswereknownwithequalcertainty,thensafelycouldbeassuredbyprovidingstrengthjustbarelyinexcessoftherequirementsoftheloads.Buttherearemanysourcesofuncertaintyintheestimationofloadsaswellasinanalysis,design,andconstruction.Theseuncertaintiesrequireasafetymargin.Inrecentyearsengineershavecometorealizethatthematterofstructuralsafetyisprobabilisticinnature,andthesafetyprovisionsofmanycurrentspecificationsreflectthisview.Separateconsiderationisgiventoloadsandstrength.Loadfactors,largerthanunity,areappliedtothecalculateddeadloadsandestimatedorspecifiedserviceliveloads,toobtainfactordeloadsthatthemembermustjustbecapableofsustainingatincipientfailure.Loadfactorspertainingtodifferenttypesofloadsvary,dependingonthedegreeofuncertaintyassociatedwithloadsofvarioustypes,andwiththelikelihoodofsimultaneousoccurrenceofdifferentloads.Earlyinthedevelopmentofprestressedconcrete,thegoalofprestressingwasthecompleteeliminationofconcreteternsilestressatserviceloads.Theconceptwasthatofanentirelynew,homogeneousmaterialthatwoukdremainuncrackedandrespondelasticallyuptothemaximumanticipatedloading.Thiskindofdesign,wherethelimitingtensilestressing,whileanalternativeapproach,inwhichacertainamountoftensileamountoftensilestressispermittedintheconcreteatfullserviceload,iscalledpartialprestressing.Therearecasesinwhichitisnecessarytoavoidallriskofcrackingandinwhichfullprestressingisrequired.Suchcasesincludetanksorreserviouswhereleaksmustbeavoided,submergedstructuresorthosesubjecttoahighlycorrosiveenvionmentwheremaximumprotectionofreinforcementmustbeinsured,andstructuressubjecttohighfrequencyrepetitionofloadwherefaatigueofthereinforcementmaybeaconsideration.However,therearemanycseswheresubstantiallyimprovedperformance,reducedcost,orbothmaybeobtainedthroughtheuseofalesseramountofprestress.Fullpredtressedbeamsmayexhibitanundesirableamountofupwardcamberbecauseoftheeccentricprestressingforce,adisplacementthatisonlypartiallycounteractedbythegravityloadsproducingdownwarddeflection.Thistendencyisaggrabatedbycreepintheconcrete,whichmagnigiestheupwarddisplacementduetotheprestressforce,buthaslittleinfluenceontheshouldheavilyprestressedmembersbeoverloadedandfail,theymaydosoinabrittleway,ratherthangraduallyasdobeamswithasmalleramountofprestress.Thisisimportantfromthepointofviewofsafety,becausesuddenfailurewithoutwarningisdangeroud,andgivesnoopportunityforcorrectivemeasurestobetaken.Furthermore,exper