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1、外文原文:TheIntroductionofcranesAcraneisdefinedasamechanismforliftingandloweringloadswithahoistingmechanismShapiro,1991・Cranesarethemostusefulandversatilepieceofequipmentonavastmajorityofconstructionprojects.Theyvarywidelyinconfiguration,capacity,modeofo
2、peration,intensityofutilizationandcost.Onalargeproject,acontractormayhaveanassortmentofcranesfordifferentpurposes.Smallmobilehydrauliccranesmaybeusedforunloadingmaterialsfromtrucksandforsmallconcreteplacementoperations,whilelargercrawlerandtowercrane
3、smaybeusedfortheerectionandremovalofforms,theinstallationofsteelreinforcement,theplacementofconcrete,andtheerectionofstructuralsteelandprecastconcretebeams.Onmanyconstructionsitesacraneisneededtoliftloadssuchasconcreteskips,reinforcement,andformwork・
4、Astheliftingneedsoftheconstructionindustryhaveincreasedanddiversified,alargenumberofgeneralandspecialpurposecraneshavebeendesignedandmanufactured.Thesecranesfallintotwocategories,thoseemployedinindustryandthoseemployedinconstruction.Themostcommontype
5、sofcranesusedinconstructionaremobile,tower,andderrickcranes.LMobilecranesAmobilecraneisacranecapableofmovingunderitsownpowerwithoutbeingrestrictedtopredeterminedtravel.Mobilityisprovidedbymountingorintegratingthecranewithtrucksorallterraincarriersorr
6、oughterraincarriersorbyprovidingcrawlers.Truck-mountedcraneshavetheadvantageofbeingabletomoveundertheirownpowertotheconstructionsite.Additionally,mobilecranescanmoveaboutthesite,andareoftenabletodotheworkofseveralstationaryunits.Mobilecranesareusedfo
7、rloading,mounting,carryinglargeloadsandforworkperformedinthepresenceofobstaclesofvariouskindssuchaspowerlinesandsimilartechnologicalinstallations.Theessentialdifficultyisheretheswingingofthepayloadwhichoccursduringworkingmotionandalsoaftertheworkisco
8、mpleted・Thisappliesparticularlytotheslewingmotionofthecranechassis,forwhichrelativelylargeangularaccelerationsandnegativeaccelerationsofthechassisarecharacteristic・InertiaforcestogetherwiththecentrifugalforceandtheCariolesforcecausethepayloadtoswinga