资源描述：
《土木专业外语大作业》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。
1、土木工程专业外语姓名：________________________学号：________________班级：_______土木1109_____________日期：_______2013.12.20____________原文：（Unit12)textBridgeFactorsActingonaBridgeBridgesarestructuresthatprovideameansofcrossingnaturalbarriers,suchasrivers,lakes,orgorges.Bridgesaredesignedtocarry
2、railroadcars,motorvehicles,orpedestrians.Bridgesalsosupportpipes,troughs,orotherconduitsthattransportmaterials,suchasanoilpipelineorawateraqueduct.Humanshavebeenconstructingbridgessinceancienttime.Theearliestbridgeswereprobablynothingmorethanfelledtreesusedtocrossriversordi
3、tches.Ascivilizationadvanced,artisansdiscoveredwaystousestone,rock,mortar,andothernaturalmaterialstoconstructlongerandstrongerbridges.Finally,asphysicistsandengineersbegantodeveloptheprinciplesunderlyingbridgeconstruction,theyincorporatedothermaterialssuchasiron,steel,andal
4、uminumintothebridgestheybuilt.Therearefourmajortypesofbridges:beam,cantilever,arch,andsuspension.Threekindsofforcesoperateonanybridge:thedeadload,theliveload,andthedynamicload.Deadloadreferstotheweightofthebridgeitself.Likeanyotherstructure,abridgehasatendencytocollapsesimp
5、lybecauseofthegravitationalforcesactingonthematerialsofwhichthebridgeismade.Liveloadreferstotrafficthatmovesacrossthebridgeaswellasnormalenvironmentalfactorssuchaschangesintemperature,precipitation,andwinds.Dynamicloadreferstoenvironmentalfactorsthatgobeyondnormalweathercon
6、ditions,factorssuchassuddengustsofwindandearthquakes.Allthreefactorsmustbetakenintoconsiderationinthedesignofabridge.WordstoKnowAbutment:Heavysupportingstructuresusuallyattachedtobedrockandsupportingbridgepiers.Bedrock:PortionofEarth’smantlemadeofsolidrockonwhichpermanentst
7、ructurescanbebuilt.Deadload:Theforceexertedbyabridgeasaresultofitsownweight.Dynamicload:Theforceexertedonabridgeasaresultofunusualenvironmentalfactors,suchasearthquakesorstronggustsofwind.Liveload:Theforceexertedonabridgeasaresultofthetrafficmovingacrossthebridge.Piers:Vert
8、icalcolumns,usuallymadeofreinforcedconcreteorsomeotherstrongmaterial,onwhichbridge
