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本科毕业设计（论文）专业名称：土木工程专业（道路与桥梁）年级班级：道桥08-5班学生姓名：指导教师：二○一二年五月十八日专业外文翻译河南理工大学本科毕业设计专业外文翻译1GeometricDesignofHighwaysTheroadisonekindoflinearconstructionusedfortravel.Itismadeoftheroadbed,theroadsurface,thebridge,theculvertandthetunnel.Inaddition,italsohasthecrossingoflines,theprotectiveprojectandthetrafficengineeringandtheroutefacility.Theroadbedisthebaseofroadsurface,roadshoulder,sideslope,sideditchfoundations.Itisstonematerialstructure,whichisdesignedaccordingtoroute'splaneposition.Theroadbed,asthebaseoftravel,mustguaranteethatithastheenoughintensityandthestabilitythatcanpreventthewaterandothernaturaldisasterfromcorroding.Theroadsurfaceisthesurfaceofroad.Itissingleorcomplexstructurebuiltwithmixture.Theroadsurfacerequirebeingsmooth,havingenoughintensity,goodstabilityandanti-slipperyfunction.Thequalityofroadsurfacedirectlyaffectsthesafe,comfortandthetraffic.HighwaygeometrydesignstoconsiderHighwayHorizontalAlignment,VerticalAlignmenttwokindsoflinearandcross-sectionalcompositionofcoordination,butalsopayattentiontothesmoothflowofthelineofsight,etc.Determinetheroadgeometry,considerthetopography,surfacefeatures,rationaluseoflandandenvironmentalprotectionfactors,tomakefulluseofthehighwaygeometriccomponentsofreasonablesizeandthelinearcombination.1.AlignmentDesignThealignmentofaroadisshownontheplaneviewandisaseriesofstraightlinescalledtangentsconnectedbycircular.Inmodernpracticeitiscommontointerposetransitionorspiralcurvesbetweentangentsandcircularcurves.Alignmentmustbeconsistent.Suddenchangesfromflattosharpcurvesandlongtangentsfollowedbysharpcurvesmustbeavoided;otherwise,accidenthazardswillbecreated.Likewise,placingcircularcurvesofdifferentradiiendtoend(compoundcurves)orhavingashorttangentbetweentwocurvesispoorpracticeunlesssuitabletransitionsbetweenthemareprovided.Long,flatcurvesarepreferableatalltimes,astheyarepleasinginappearanceanddecreasepossibilityoffuture河南理工大学本科毕业设计专业外文翻译2obsolescence.However,alignmentwithouttangentsisundesirableontwo-laneroadsbecausesomedrivershesitatetopassoncurves.Long,flatcurvesshouldbeusedforsmallchangesindirection,asshortcurvesappearas“kink”.Alsohorizontalandverticalalignmentmustbeconsideredtogether,notseparately.Forexample,asharphorizontalcurvebeginningnearacrestcancreateaseriousaccidenthazard.Avehicletravelinginacurvedpathissubjecttocentrifugalforce.Thisisbalancedbyanequalandoppositeforcedevelopedthroughcannotexceedcertainmaximums,andthesecontrolsplacelimitsonthesharpnessofcurvesthatcanbeusedwithadesignspeed.Usuallythesharpnessofagivencircularcurveisindicatedbyitsradius.However,foralignmentdesign,sharpnessiscommonlyexpressedintermsofdegreeofcurve,whichisthecentralanglesubtendedbya100-ftlengthofcurve.Degreeofcurveisinverselyproportionaltotheradius.Tangentsectionsofhighwayscarrynormalcrossslope;curvedsectionsaresuperelevated.Provisionmustbemadeforgradualchangefromonetotheother.Thisusuallyinvolvesmaintainingthecenterlineofeachindividualroadwayatprofilegradewhileraisingtheouteredgeandloweringtheinneredgetoproducethedesiredsuperelevationisattainedsomedistancebeyondthepointofcurve.Ifavehicletravelsathighspeedonacarefullyrestrictedpathmadeupoftangentsconnectedbysharpcircularcurve,ridingisextremelyuncomfortable.Asthecarapproachesacurve,superelevationbeginsandthevehicleistiltedinward,butthepassengermustremainverticalsincethereisoncentrifugalforcerequiringcompensation.Whenthevehiclereachesthecurve,fullcentrifugalforcedevelopsatonce,andpullstherideroutwardfromhisverticalposition.Toachieveapositionofequilibriumhemustforcehisbodyfarinward.Astheremainingsuperelevationtakeseffect,furtheradjustmentinpositionisrequired.Thisprocessisrepeatedinreverseorderasthevehicleleavesthecurve.Wheneasementcurvesareintroduced,thechangeinradiusfrominfinityonthetangenttothatofthecircularcurveiseffectedgraduallysothatcentrifugalforcealsodevelopsgradually.Bycarefulapplicationofsuperelevationalongthespiral,asmoothandgradualapplicationofcentrifugalforcecanbehadandtheroughnessavoided.河南理工大学本科毕业设计专业外文翻译3Easementcurveshavebeenusedbytherailroadsformanyyears,buttheiradoptionbyhighwayagencieshascomeonlyrecently.Thisisunderstandable.Railroadtrainsmustfollowtheprecisealignmentofthetracks,andthediscomfortdescribedherecanbeavoidedonlybyadoptingeasementcurves.Ontheotherhand,themotor-vehicleoperatorisfreetoalterhislateralpositionontheroadandcanprovidehisowneasementcurvesbysteeringintocircularcurvesgradually.However,thisweavingwithinatrafficlane(butsometimesintootherlanes)isdangerous.Properlydesignedeasementcurvesmakeweavingunnecessary.Itislargelyforsafetyreasons,then,thateasementcurveshavebeenwidelyadoptedbyhighwayagencies.Forthesameradiuscircularcurve,theadditionofeasementcurvesattheendschangesthelocationofthecurvewithrelationtoitstangents;hencethedecisionregardingtheiruseshouldbemadebeforethefinallocationsurvey.TheypointofbeginningofanordinarycircularcurveisusuallylabeledthePC(pointofcurve)orBC(beginningofcurve).ItsendismarkedthePT(pointoftangent)orEC(endofcurve).Forcurvesthatincludeeasements,thecommonnotationis,asstationingincreases: