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1、13LesterdiagramWiththedevelopmentofthenetworkgrid,thedraftingofanarrowdiagramenablestheactiv-itiestobeeasilyorganizedintodisciplinesorworkareasandeliminatestheneedtoenterreferencenumbersintothenodes.Insteadthegridreferencenumbers(orletters)canbefedintothecomputer.Thegridsystemalsomakesitpossible
2、toproduceacceptablearrowdiagramsonacomputerwhichcanbeused‘inthefield’withoutconvertingthemintotheconventionalbarchart.Anexampleofsuchacomputerizedarrowdiagram,whichhasbeendevelopedbyClare-montControlsaspartoftheirlatestHornetWindmillprogram,isgiveninFigure13.1.Itwillbenoticedthatthelinklinesneve
3、rcrossanode!Agridsystemcan,however,poseaproblemwhenitbecomesnecessarytoinsertanactivitybetweentwoexistingones.Inpractice,resource-fulplannerscanovercometheproblembycombiningthenewactivitywithoneoftheexistingactivities.If,forexample,twoadjoiningactivitieswere‘CastColumn,4days’and‘CastBeam,2days’a
4、nditwerenecessarytoinsert‘StrikeFormwork,2days’betweenthetwoactivities,theplannerFigure13.1ProjectPlanningandControlFigure13.2wouldsimplyrestatethefirstactivityas‘CastColumnandStrikeFormwork,6days’(Figure13.2).Whilethisovercomesthedraftingproblemitmaynotbeacceptablefromacostcontrolpointofview,es
5、peciallyifthenetworkisgearedtoanEVAsystem(seeChapter27).Furthermorethefactthatthegridnumberswereonthenodesmeantthatwhenitwasnecessarytomoveastringalongoneormoregridspaces,therelationshipbetweenthegridnumberandtheactivitychanged.ThiscouldcomplicatetheEVAanalysis.Toovercomethis,thegridnumberwaspla
6、cedbetweenthenodes(Figure13.3).Figure13.3ItcanbearguedthataprecedencenetworklendsitselfadmirablytoagridsystemasthegridnumberisalwaysandpermanentlyrelatedtotheactivityandisthereforeidealforEVA.However,theproblemofthecongestedlinklines(especiallytheverticalones)remains.Now,however,theperfectsoluti
7、onhasbeenfound.ItisineffectacombinationofthearrowdiagramandtheprecedencediagramandlikethemarriageofHenryVIIwhichendedtheWarsoftheRoses,thismarriageshouldendthewarofthenetworks!90LesterdiagramFigure13.4Thenewdiagram,whichcoul
