project scheduling & control...(a-on-a), or arrow diagram • activities are represented as...
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PROJECTSCHEDULING&CONTROL
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ProjectPlanningvsProjectSchedulingProjectControlNetworkModelPrecedenceDiagrams
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Example
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IntroductiontoTechniques• Planningcanbethoughtofasdetermining“what”isgoingtobedone,“how,” “where,”andby“whom”
• Ownerswanttheirprojectscompletedwithinspecifiedtimeandbudgetconstraints
• ManagementoftimeandcostdidnotevolveasascienceuntilaftertheIndustrialRevolution
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• Thescienceof“scheduling”iscommonlyreferredtoasthecriticalpathmethod(CPM)in1956-57• Thearrowdiagrammingmethod(ADM)resulted
• Theprogramevaluationreviewtechnique(PERT)wasdevelopedthesametimebytheU.S.Navy
• ADMwasdeterministicandPERTwasprobabilistic
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TheadventofPCsinthe1980sledtoalargenumberof
PC-basedschedulingsystemsAtthelow-costend(Timeline)
andthehigh-costend(Primavera)
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PlanningandScheduling• Thereisasignificantdifferencebetween“planning”and“scheduling”• Oftenusedinterchangeably—whichisamisuse
• Schedulingcanneverbeperformedeffectivelywithoutplanning
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PlanningandScheduling
Theplanningportionofaconstructionprojectrelatestodevelopingthelogic
ofhowaprojectwillbeconstructedSchedulingconsistsofintegratingthat
planwithacalendarorspecifictimeframe
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PlanningandScheduling• Wealldoplanningandschedulingonaregular,informal,basis• Oftenitisnecessarytocreatea“to-dolist”
• Asthenumberofitemsincreasesand/ortimeframeexpands,weputourlistinthecontextoftime
• Planningandschedulingisdoneextensivelyandformallyonconstructionprojects• BeginningwiththeNoticeofAward
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PlanningandScheduling
Schedulingconsistsofdeterminingthetimeneededforeachoftheplannedtasksandtheoveralllength
oftheprojectschedule
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BarChartsHenryGanttdevelopedamethodofrelatingalistofactivitiestoatimescaleinaveryeffectivemanner,bydrawingbarcharts
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BarChartsHenryGanttdevelopedamethodofrelatingalistofactivitiestoatimescaleinaveryeffectivemanner,bydrawingbarcharts
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BarCharts• Barchartsaresimplepresentationsthatshowwhenmajorworkactivitiesarescheduled
• Mostcommonlyemployedandreadilyrecognizedschedulingmodelsinusetoday
Asimpleschedulecaneasilybeshowninnetworkform
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BarCharts
Barchartsarethemostpopularmeansbywhichschedulinginformationiscommunicatedin
theconstructionindustryWidespreaduseisbestattributedtotheeasewithwhichtheycanbe
understoodwithacursoryexamination
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ShortcomingsofBarCharts• Barchartsbegintofailtoprovidevaluableinformationwhenprojectsbecomemorecomplex• Ageneralcriticismofbarchartsisthattheydonotshowcleardependenciesbetweenactivities• Whilethestatusofindividualactivitiescanbeascertained,overallprojectstatuscannotbecertain(Whensomeactivitiesarenotonschedule)• Changesinthelogicalsequencingofactivitiesinabarchartcannotbereadilymade• Especiallywhenmanyactivitiesareinvolved
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ShortcomingsofBarCharts
Barchartshortcomingsvirtuallydisappearwhenschedulingsoftwareisused
Mostpopularcomputergeneratedschedulespermiteasyconversionbetween
precedencediagramsandbarcharts
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ValueofBarCharts• Amajorstrengthofbarchartsistheabilitytoclearlyandquicklypresentthestatusofaproject
• Noextensivetrainingisrequiredtolearnhowtoextractinformationfromthem
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SchedulingNetworks• Barchartshavebeensurpassedbynetworksasschedulingtools—especiallyonlargerprojects• Anetworkrepresentsamodel,orplan,oftheprojectasitisproposedtobeundertaken• Eachactivityisassignedduration;calculationsthroughthenetworkprovideasingle,specificdurationfortheprojectasawhole• Itisimportanttorecognizethedistinctionbetweendurationandevent
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SchedulingNetworks
Aneventisthepointintime,oraninstantatwhichthestatusofcompletionofaprojector
activitycanbedefinedThedurationofanactivityisthetimethatwillbe
consumedincompletingatask
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SchedulingNetworks• CPMidentifieschainsofactivitiesintheprojectthatcontrolhowlongtheprojectwilltake• AtraditionalCPMtechniqueistheActivity-on-Arrow(A-on-A),orarrowdiagram• Activitiesarerepresentedasarrowsorlines
• ThealternativeapproachisActivity-on-Node(A-on-N),referredtoasthePrecedencetechnique• PERTcanbethoughtofasa“generalized”CPM• Inwhichan“expected”activitydurationiscomputed
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SchedulingNetworks
PERTisusedprimarilyinundertakingswhereinsufficientexperienceorhistoricaldataare
availableforestimatingdurationsofindividualactivitiesinaproject
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OtherSchedulingApproaches• Amatrixscheduleisoneinwhichaspreadsheetisusedtoshowallactivitiesonaparticularproject• Itassumeseachprojectwillconsistofthesameactivities
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OtherSchedulingApproaches
Seepage9
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OtherSchedulingApproaches
Aformofschedulingthatshowslessdetail
isthe“horseblanket”
Itiseasytoseeataglancehowmucheffort
istobeexpendedonaprojectthroughits
evolution—fromplanningtofinaloccupation&use CE
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WorkBreakdownStructure• Mostprojectsforwhichformalschedulesareusedaredefinedwithhundredsorthousandsofactivities• Itisimportantthatthelogicbecarefullylaidoutandthatallimportanttasksareincludedintheschedule• Whenthetasksbecomenumerous,thescheduledevelopmentcanbecomemorehaphazard,• Omissionsaresuretooccur CE
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WorkBreakdownStructure
Thescheduleconsistsoftasksthatmustbeperformed—tocompletetheproject
Thescheduleisdominatedbyverbs—thingstodo—tasks
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WorkBreakdownStructure• AWorkBreakdownStructure(WBS)isasystematicwaytodescribecomponentsofaprojectschedule• DevelopingtheWBSbeginswiththedefinitionofthemajorsystemsorcomponentsofaproject• Eachsystemisdefinedingreaterandgreaterdetail• Untilthereexistsadiscreteormeasurablepieceofworkandasingleresponsibility—workpackages
• Workpackagescanbeviewedasminiprojectsthatarecontainedwithintheentireproject
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WorkBreakdownStructure• Informationshouldbeprovidedbyvariousindividuals• Projectmanager;jobsuperintendent;others
• WBSdivides&subdividesaprojectintodifferentcomponents—area,phase,function,orothermeans• ByusingtheWBSapproach,theprojectwillbecomeeasiertocomprehend• WBSisthebackboneoftheprojectcontrolortrackingsystem
• TheWBSisanorderlypresentationofthetasksthatmustbeperformedtocompleteaparticularproject
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WorkBreakdownStructure• OnatypicalconstructionprojecttheWBSconsistsofnumerouscategories—dependingoncomplexity
WorkBreakdownStructureforaStorageFacilityProject
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WorkBreakdownStructure• Ingeneralterms,theWBScanbeviewedasarepresentationofthephysicalbreakdownoftheworktobeperformed
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ReasonsForPlanning&Scheduling• ManyprojectcontractdocumentsexpresslyrequirecontractorstosubmitaCPManalysispriortocommencingwork• InsomecasesCPManalysisisrequiredwiththebid• CPMallowstheusertoexaminethetrade-offbetweenthetime&costrequiredforaproject• Byaccuratelymonitoringprojectstatus,decisionscanbemaderegularlyaboutscheduleviability
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ReasonsForPlanning&Scheduling
MostpartiesintheconstructionprocesscanbenefitfrommakinguseofCPM
asaroutineelementofthemanagementofalloftheirprojects
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CHAPTER1END
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NetworkDiagram
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DevelopingaNetworkModel• Networkmodeldevelopmentisthemostimportantstepinusinganetworkasaschedulingtool
• Anill-preparedmodelservesnousefulpurposeandmaycompromiseconstructionprogress
StepsInBuildingaNetworkModel• Defineactivities;Orderactivities• Establishactivityrelationships;drawanetworkdiagram• Determinequantities;assigndurationstoactivities• Assignresourcesandcosts• Calculateearlyandlatestart/finishtimes• Computefloatvaluesandidentifythecriticalpath• Scheduleactivitystart/finishtimes
DefiningActivities• Production/Construction• Procurement• Management• ObjectiveoftheModel
OrderingActivities• Foreachidentifiedactivity,thefollowingmustbedetermined:• Whichactivitiesmustprecedeit?• Whichactivitiesmustfollowit?• Whichactivitiescanbeconcurrentwithit?
OrderingActivities
Constraintsexistintherealworld—andmustbeconsideredinorderforanetworktobeuseful
– PhysicalConstraints– ResourceConstraints– ProductivityConstraints– SafetyConstraints– FinancialConstraints
– EnvironmentalConstraints– ManagementConstraints– ContractualConstraints– ProductivityConstraints– RegulatoryConstraints
OrderingActivities• Introductionofexcessiveconstraintsinnetworklogiccanhavethefollowingimpactsonaproject:• Reduceschedulingflexibility• Lengthenprojectduration• Generallyincreaseprojectcost• Confusebasicschedulinglogic
DrawingtheNetworkDiagram• Theprecedencediagramisacommonlyusedtypeofnetworkdiagram
• Mostpopularsoftwarecurrentlyusedforcomputerschedulingsupportsonlyprecedencediagrams
DrawingtheNetworkDiagram
SimpleExampleofaPrecedenceDiagramforErectingaConcreteWall
Theprecedencediagramis“read”fromlefttoright
DrawingtheNetworkDiagram
ExampleofaPrecedenceDiagramforConstructingaConcreteFooting
DrawingtheNetworkDiagram• Activitiesconsumetime,andeventssimplyoccuratapointintime
• Thepointintimeatwhichanactivitycanstartmaybeconsideredanevent
• Thepointintimeorinstantatwhichanactivityiscompletedcanalsobeconsideredanevent
AssigningDurationstoActivities• Thedurationofanactivityistheestimatedtimethatwillberequiredtocompleteit• Typically,inconstruction,theunitoftimeisdays
• Itisassumedworkisperformedonacontinuousanduniformbasis• Withinthestandardworkdayandworkweek
AssigningDurationstoActivities• Durationscanfrequentlybedirectlyrelatedtolaborcostestimatesforthetasks
Costestimatesmaybedevelopedasfollows:
Durationoftheactivityisassumedtobe:
AnalternativeistousehistoricaldataQuantitativedatafromactualprojectsthefirm
haspreviouslyundertaken
AssigningDurationstoActivities
Themajorrequirementforassignmentofresources&coststoindividualactivities
isacleardescriptionoftherelationshipCPMactivitiesandtheunits/phasesof
workbywhichtheestimateisdeveloped
AssigningResourcesandCosts
CalculatingEarly/LateStart/FinishTimes
• Thelatestarttimeisthelatestanactivitycanstartwithoutadverselyimpactingthecompletiondate
• Theearlyfinishtimeistheearliestanactivityisexpectedtobecompleted• Thelatefinishtimeisthelatestanactivitycanbecompleted
IdentifytheCriticalPath
Iftheactivitystartslaterthantheassigneddate,ortakeslongertocompletethanthe
assignedduration,theprojectcompletiondatewillbeextended
bythesameamountoftime
IdentifytheCriticalPath• Whenanactivitystartdateisfixedinthisway,theactivityissaidtohavenofloat
• Suchactivitiesaresaidtobe“critical”• Meaninganydelayinthestartdateorcompletiondatewillextendtheprojectduration
SchedulingActivityStart/FinishTimes
• Thenetworkandtheinformationgeneratedforeachoftheactivitieswillbeusefulformanagementtoexecutetheprojectrequirements
• Managementdecisionsrevolvearoundtheuseofanyflexibilityorfloatthattheactivitiespossess
TheNetworkDiagram-bringingordertoprojectworkflows.
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ANetworkDiagramisagraphicalwaytoviewtasks,dependencies,andthecriticalpathoftheproject.Boxes(ornodes)representtasks,anddependenciesshowupaslinesthatconnectthoseboxes.Inthecontextofprojectplanning,anetworkdiagramisasequenceofsteps(activities),commonlyrepresentedbyblocks,thatarelinkedtogetherinthelogicalsequencetheyneedtobecarriedout.ProducinganetworkdiagramfollowsthecompletionofyourprojectWorkBreakdownStructure.Thepileofpost-itsthatyouhavesavedfromtheWBSexercisegetsputtogooduseindevelopinganetworkdiagram.Oncethelogicdiagramhasbeencompleted,youhaveaclearerpictureoftherequiredsequenceofeventsandactivitiesforyourproject.
TheNetworkDiagram-bringingordertoprojectworkflows.
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AllthelogiclinksinthissimpleexamplearereferredtoasFinish/Startlogiclinks.Thesucceedingactivitycannotstartuntiltheprecedingactivityhasfinished.Typesoflogiclinks:Start/Start-whenoneactivitystarts,anotherindependentactivitymuststart.Finish/Finish-twoactivitiesmustfinishatthesametime.Finish/Startwithalag-thesucceedingactivitymuststartsomedefinedtimeaftertheprecedingactivityhasfinished.Start/Startwithalag-whenoneactivitystarts,anothermustalsostartafteradefinedtime.
TheNetworkDiagram-bringingordertoprojectworkflows.
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IMPORTANT:Alwaysfollowtherule-havetheminimumnumberofactivitiesneededtoproperlyunderstandthesequencing.Onlyaddmoredetailifitbenefitsthelevelofunderstandingorfutureprogresscontroloftheprojectactivitylist.
NetworkModel
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SampleNetworkDiagram
ActivityNetworkDiagram
Overview• DefinitionofanActivityNetworkDiagram• History• BasicTerms• Howcanitbeusedinyourorganization?• Howthediagramworks• Example• ActivityNetworkDiagramExercise• Summary
DefinitionofanActivityNetworkDiagram• AlsoknownastheProgramEvaluationReviewTechnique(PERT)orCriticalPathDiagram
• Toolusedtocontrolthelengthofprojects• Takesintoaccountmanyaspectsofprojects:tasktimes,slacktimes,criticaltasks,etc.
DefinitionofanActivityNetworkDiagram(cont.)
• Designedforresearchanddevelopment-typeprojects• Determinesaprobabilitydistributionforaproject
History• DevelopedbytheU.S.DepartmentofDefense• Firstusedasamanagementtoolformilitaryprojects• Adaptedasaneducationaltoolforbusinessmanagers
BasicTermsBasicVocabularyofthePERTDiagram:• Activity–partoftheprojectrepresentedbyanarroworline
• BestEstimate(B)–earliestcompletiontime• Criticalpath(CP)–themosttimeconsumingpaththroughthediagramwithnoslacktime
• EarliestStartTime(EST)–earliestpossibletimeforanactivitytobegin
• Network–theprojectshowngraphically• Mostlikelyestimate(M)–lengthoftimeprobablyneeded
BasicTerms(cont.)• ExpectedTime(ET)–theaveragedurationtime• Event–representsthestartorfinishofoneormoreevents(shownasacircle,square,orothersymbol)
• LatestStartTime(LST)–latesttimeanactivitycanbeginandstillbecompletedbeforethenextactivity
• SlackTime–lateststarttimeminusearlieststarttimeforanactivity
• Worstestimate(W)–pessimistictimeestimate
Howcanitbeusedinyourorganization?Brainstormideasofwhereactivitynetworkdiagramscouldbeutilizedinyourbusinesspractices…
Howcanitbeusedinyourorganization?• Findingminimumcompletiontimes
• Determiningmaximumcompletiontimes
• Valueoftimeforeachstepintheproject
• Assigningspecifiedtimesforpartsoftheproject
• Createsarealisticscheduleforthecompany
HowthediagramworksBasicRules:• Allprecedingactivitiesmustbecompletedbeforethe
projectcanbegin• Thearrowsrepresentthelogicalprecedenceoftheproject
HowtheDiagramWorks(Cont.)
Procedurefordevelopment: 1. Identifyallactivitiesandrelationshipsamong
them2. Sketchthediagram3. Estimatethetimesforeachactivity,ornode,
inthediagram4. Determinethecriticalpath5. Evaluatethediagramformilestonesandtarget
datesintheoverallproject
BegintheAnalysisØ RememberyourstepsforPERTdiagrams:
Ø Usingthegivendiagram,listallthesteps
Ø Determinetasktimes
Ø Determinerelationshipsbetweenthetasks
Ø Findtheearlieststarttime
Ø Findthelateststarttime
Ø Determineslackandthecriticalpath
AdvantagesofPERTDiagrams• Projectingplansbeforetheybegin• Helpstoseparateplanningandschedulingfunctionsofaproject
• Controlsprojects• Clarifiesmaintenanceoftheplan• Showsdependencyofdifferentaspectsoftheproject
AdvantagesofPERTDiagrams• Allowsforconcentrationonthestepsthemselvesandnotthetimerequiredforeach
• Representsarealisticschedule• Focusesattentiononcriticalaspectsoftheplan• Changescanbemadeeasilyintheproject
DisadvantagesofPERTDiagrams
• Cannothandleallspecificproblemsthatariseineachstepoftheproject
• Differentgraphicalrepresentationscanbemadeeasierinothertypesofcontrolprocesses
OddsandEndsü ActivityNetworkDiagramshavemanymoreadvantagesthandisadvantages
ü Theyareusedinalltypesofbusinessesü Thetopicsthatwerecoveredshouldactasthekeyinhelpingyouleadyourcompanyintheirnextbusinessproject
PrecedenceDiagram
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Precedence(Activity-on-Node)Networks
• Themostcommontypeofnetworkscheduleinusetodayistheprecedencediagram• Aseriesofnodeswithlines(links)connectingthemtoillustrateactivities
Activitiesarerepresentedbynodes,drawninanydesiredshape
Linesrepresent“Activitylinks,”usedtorepresentdependenciesbetweenactivities
ActivityRelationships
Useofvarioustypesofrelationshipsbetweenactivitiesmakesitpossibleto
prepareschedulesthataccuratelyportraythetruerelationshipsbetweenactivities
ActivityRelationships• Finish-to-start(FS)—eachactivitydependsonthecompletionofitsprecedingactivity
TypicalSequenceofFinish-to-StartRelationships
ActivityRelationships• TheseactivitiesmightalsobeshownasbeingrelatedbyFinish-to-Startwithadelay
Finish-to-StartRelationshipwitha28-DayDelay
ActivityRelationshipsFinish-to-Finish(FF)
ActivityRelationships
Finish-to-StartRelationshipforWindowInstallation
Finish-to-Finish(FF)—withDelay
ActivityRelationshipsActivitieswithFinish-to-Finish
withaDelayRelationships
ActivityRelationshipsActivitieswithStart-to-StartRelationships
ActivityRelationshipsActivitieswithStart-to-StartwithaDelayRelationships
ActivityRelationshipsActivitieswithStart-to-StartwithaDelayRelationships
ActivityRelationshipsActivitieswithStart-to-Startand
Finish-to-FinishRelationships
ActivityRelationshipsSequenceofStart-to-FinishwithaDelay
ActivityRelationshipsStart-to-FinishwithaDelay—Relationships
ActivityRelationshipsStart-to-FinishwithaDelay—Relationships
ActivityRelationshipsStart-to-FinishwithaDelay—Relationships
BasicsaboutPrecedenceDiagrams• Donotconfusethelinklineswithactivities• Nodesorprecedenceactivitiescanbedenotedsimplybyasinglecharacter• Generallycustomizedtotheuser’sconvenience
ExampleNodeDesignation
SimplifiedFormatforaPrecedenceActivity
ActivityRelationships
Apreliminaryorroughnetworkcanbegeneratedbypositioningeachactivityrelativetoother
activitiesanddrawinglinesbetweeneachsetofrelatedactivities
BasicsaboutPrecedenceDiagrams• Amoresystematicapproachusessequencesteps• Eachactivityisassignedtoaparticularsequencestep
BasicsaboutPrecedenceDiagrams
Lagistimeassociatedwithalinkline
Itindicatesthedifferencebetweentheearlyfinishoftheactivityprecedingthelinkand
theearlystartoftheactivityfollowingthelink
Lagisnotthesameasleadtimeordelayassignedtoalink
ActivityRelationships
Linklagvaluesareusefulindeterminingfreefloatandtotalfloatofanactivity
However,linklagvaluesshouldnotbeconfusedwithfloat
CalculationsOnaPrecedenceNetwork
• EarlyActivityStart(ES):Earliesttimeanactivitycanstart—asdeterminedbythelatestoftheearlyfinishtimesofallIPAs
• EarlyActivityFinish(EF):Earliesttimeanactivitycanfinish—determinedbyaddingthedurationoftheactivitytotheearlystarttime
• LateActivityStart(LS):Latesttimeanactivitycanstartwithoutdelayingtheprojectcompletion
• LateActivityFinish(LF):Latesttimeanactivitycanbefinishedwithoutdelayingprojectcompletion
CalculationsOnaPrecedenceNetwork
• EarlyEventOccurrenceTime:Earliestaneventcanoccur—determinedbythelatestearlyfinish
• LateEventOccurrenceTime:Latestaneventcanoccur• FreeFloat:Amountoftimeanactivitycanbedelayedbeforeitimpactsthestartofanysucceedingactivity
• TotalFloat:Amountoftimeanactivitycanbedelayedbeforeimpactingprojectcompletiondate
CalculationsOnaPrecedenceNetwork
• LAG:Theamountoftimethatexistsbetweentheearlyfinishofanactivityandtheearlystartofaspecifiedsucceedingactivity
CalculationsOnaPrecedenceNetwork
IllustratingcomputationsonaprecedencediagramAllrelationshipsareassumedtobeFinish-to-Start
EarlyTimes(EarlyStart[ES]andEarlyFinish[EF])
CalculationsOnaPrecedenceNetwork
• 1.Assign1astheearlystartdateofthefirstactivity• 2.Calculatetheearlyfinishtimefortheactivity• 3.Theearlystartofactivitieswillbedeterminedbytheearlyfinishtimesofprecedingactivities• Otherthanthefirstactivityoractivities
• 4.Repeatsteps2and3foreachnetworkactivityuntilES&EFaredeterminedforthelastactivity
CalculationsOnaPrecedenceNetwork• 5.CalculatelagsforeachlinkbydeterminingthedifferencebetweentheESofeachactivityfollowingalinklineandtheEFoftheactivitythatprecedesit
CalculationsOnaPrecedenceNetwork
• 6.Determinethefreefloatofanactivityasbeingequaltothesmallestlagvalueofalllinksleavingfromthatactivitynode
• 7.Assignavalueof0totalfloat(TF)tothelastactivityinthenetwork
• 8.Thetotalfloatvaluesfortheactivitiesinthenetworkcannowbedetermined
CalculationsOnaPrecedenceNetwork• 9.Proceedinabackward-passfashionuntilyouhavecomputedtheTFforallactivities
CalculationsOnaPrecedenceNetwork• 10.Determinelatestarttimesforalloftheactivities
CalculationsOnaPrecedenceNetwork• 11.Totalfloatisaddedtotheearlyfinishofeachactivitytodeterminethelatefinishofeachactivity
ActivityRelationships
Oncetheearlyandlatestarttimes,earlyandlatefinishtimes,freefloat,andtotalfloatofall
activitiesaredetermined,thecalculationsarecompleted
CalculationsOnaPrecedenceNetwork
Aslightlymoreinvolvedprojectshowstheprecedencediagramforconstructingatenniscourtfacility
IndependentFloatandInterferingFloat
• Independentfloatisfloat“owned”exclusivelybyoneactivity—alsocalled“safe”float,• Flexibilityascribedtothespecificusebyoneactivity
IndependentFloatandInterferingFloat
SimpleNetworktoDetermineIndependentFloat
IndependentFloatandInterferingFloat
• Interferingfloatisfloatanactivitymayhave,subjecttousebyotheractivities—calledsharedfloat• Differencebetweenitstotalfloatanditsfreefloat
IndependentFloatandInterferingFloat
SimpleNetworktoDetermineInterferingFloat
Different-ActivityRelationshipsCalculationscanalsodeterminetheschedulinginformationforother-
activityrelationships
Asimplefinish-to-startrelationshipofthisnetwork,consistingofActivitiesI,J,andK
Different-ActivityRelationshipsEarlystart/finishtimesarecomputedby
conductingaforwardpassthroughthenetwork
Latestart/finishtimesarecomputedbyconductingabackwardpassthroughthenetwork
Different-ActivityRelationships
Thesimplenetworkismademorecomplicatedwhenthesubjectoflagisintroducedtotheactivityrelationships
ComputationsforaFinish-to-Startrelationshipwiththeincorporationoflagvalues
Different-ActivityRelationships
Start-to-Startrelationshipwithlagvalues
Different-ActivityRelationships
Finish-to-Finishrelationshipwithlagvalues
Different-ActivityRelationships
Start-to-Finishrelationshipwithlagvalues
Different-ActivityRelationships
Withdetailedschedulinginformationabouteachactivity,informeddecisionscanbemadewhenthe
needarisestoacceleratetheschedule,makechangesinthe
network,orredefinetheschedulinglogic
DeterminingActivityDurations
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DETERMININGACTIVITYDURATIONS• Developmentanduseofschedulesreliesheavilyonactivitydurations
• Somedegreeofuncertaintyisalwayspresent• However,areasonableeffortshouldprovideacceptableresult
ESTIMATING• Anestimateis—atbest—acloseapproximationoftheactualcost
• Aprojectcostestimateisuniquetothatproject• Evenwhencomparedtoother,similarprojects
• Soundnessofthecompletedestimatedependson:• Accuracyofthequantitytake-offand• Judiciousselectionofunitcostsandproductionrates
TypesOfEstimates• Conceptualestimatesareoftenusedbyanownertodeterminetheapproximatecostofaproject• Beforemakingafinaldecisiontoconstructit
• Detailedestimatesaregenerallypreparedbycontractors• Priortosubmittingbidsoncompetitivelybidcontracts• Whenenteringlump-sumorfixed-pricecontracts
ConductingADetailedEstimate• Theprocessbeginswithananalysisofphysicalquantitiestobeincorporatedinthefinalproject
• Costsaregenerallycapturedseparatelyformaterials,equipment,labor&subcontracteditems• Separatetake-offsaremadeforeachjobitem
• Take-offs,ingeneral,followthesamesequenceasusedtoperformtheactivities
• Itisgoodpracticetocheckthetake-offtoensurethatnojobquantitieshavebeenoverlooked• Andnootherobviouserrorshavebeenmade
ConductingADetailedEstimate• Foradetailedestimate,well-definedcostsmustbelinkedtoeachoftheitemsinthequantitytake-off
• Oncequantitieshavebeenpriced,anestimateismadeforjoboverhead,andhome-officeoverhead
• Formanyoverheaditems,itisessentialthatanaccurateestimatebemadeoftheprojectduration
• Manyprojectcostsareadirectfunctionoftheamountoftimerequiredtocompletetheproject
Theestimateshouldformthefoundationsonwhichthe
scheduleisactuallybased
ConductingADetailedEstimate
EstimatingDurations• Themethodusedtoestablishdurationofanactivitydependsonthesizeoftheactivity• Andtheamountofaccuracyrequired
• Schedulerswithsignificantrelevantexperiencemaybeabletomakeagoodguess• Mostopttoanalyzetheoperationindetail
• Aschedulercanconsiderperformancesonpastprojects,andthusmakethedurationestimates• Withoutactuallyperforminganydetailedanalysis
EstimatingDurations• Whenhistoricaldataareused,theinformationofprimaryinterestwillbetheproductivityrates
• Onshortdurationactivities,asignificantpercentageoftimecanbedevotedtomobilizationallowances
• Referenceguidesthatgiveproductivityestimatesforvarioustasksareavailable• Generallyconservativeintheirestimates
• Durationsaregenerallyrecordedintermsofwholedays
SchedulingIssues• Inactualscheduling,averybasicapproachistouseeitheran“earlystart”ora“latestart”schedule
• Majoractivitiesshouldbeexaminedtodeterminethetimeoftheyeartheyarescheduledtooccur
• Theprojectmanagershouldalsotrytoanticipaterework,andlossofsometimeduetoinspections
SchedulingIssues• Theseschedulesmaybeusedtopredictcashflowrequirementsontheproject
• Expendituresdonotnecessarilyimplyprogressisbeingmade,oraspecificprofithasbeenearned• Itismerelyanindicationoftotalprojectexpenditures
Apoorcashpositionmaybehandledbyschedulingparticularlyexpensivenoncritical
activitiesaslateaspossibletodeferthelargepaymentfortheitem
SchedulingIssues
FactorsInfluencingChoiceofActivitySchedules
• Schedulingshouldsatisfyconstraintsimposedbythecontractorbyspecificneedsofthefirm
• Staggeringdeliveriescanreducejobsitecongestionandsimplifycoordinationefforts
• Thescheduleshouldreflectanysignificantconcernsrelatedtomaterials
• Theinitialscheduleisimportanttoarrangementsforsubcontractorstartdates,contract-specifiedmilestonedates,etc.
WeatherandtheSchedule• Weatherconsiderationsorothercontingenciesmaybeincorporatedintoaschedule
• Durationsofweather-dependentactivitiescanbeincreasedpriortonetworkcalculations
• Anothermethodofweatherinclusionistoinsertoneormorespecificactivitiesintothenetworklabeledasweatherdelays
• Amoreseriousconsiderationforthescheduleriswhenthecontractstipulatesthatcontractdurationreflectstheimpactofadverseweather
Afurtherconsiderationiswhetherthecontractisadministeredonthebasisofworkingdays
orcalendardays—andhowweatheraffectsthedefinitionofworkingdays
WeatherandtheSchedule
UncertaintyinDurationEstimates• Whenmostschedulesaredeveloped,activitiesareassumedtobefixedataparticularduration
• Anappreciationofthetruemeaningofadurationestimaterequiresarudimentaryunderstandingofprobabilityandstatistics
• Thedesiredestimateshouldbeararealisticvalue• Thatdoesnotgenerallyunderstatetheduration
• Therelevantinformationneededtoestimatewithconfidencearethemean&standarddeviations
UncertaintyinDurationEstimates• Thestandarddeviationimpliestheamountofvariabilitythatexistsinacollectionofnumbers
• Contractorsmustcomputearealisticdurationorhaveaverygoodintuitivesenseoftheappropriateestimatetobeused
TimeinContactProvision
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Decisionsaboutprojectsequencesandthecontractor’sapproachinundertaking
aprojectareimpactedbythecontractuallanguage
TimeinContractProvisions
TimeinContractProvisions• Thecontractincludesprovisionsthatrelatedirectlytotheproject’sduration
• Otherprovisionsaddresstimingoftheowner’scashdisbursementstothecontractor
• Someprovisionsmaystipulatetheschedulingtechniquethatmustbeusedonaproject
• Thedegreeofriskshouldlogicallybereflectedintheamountofthebid
TimeisofTheEssence• Allpartiestothecontractshouldconsidertimeasanelementalaspectofthecontract
• Emphasisontimegivesgreatervaliditytotheinclusionofliquidateddamagesprovisions• Italsoallowsownerstopursueclaimsforbreachofcontract
RequirementsforProjectCoordination• Theownermaystipulatethatmajorpartiesdiscusstheproject’soverallorganizationpriortothestartofanyconstructionwork
• Whenitcomestocooperation,theissuecannotbeunilateral—bothpartiesmustberesponsible
• Subcontractorsmustknowwhentheirservicesareneeded,andmustrespondattheappropriatetime• Sotheconstructioneffortprogressessmoothly
Cooperation• Dependingonthenatureoftheproject,thesitemaybeusedbypartiesotherthanthecontractor
• Ifdualoccupancyorfacilityuseisanticipated,aprovisionthatstipulatesthatthecontractoristocooperatewiththeseotherpartiesisprudent
• Itisalsoimportantfortheownertotrytoconveythespecificnatureoftheworkbeingperformedbytheotherparties
ProgressSchedule• Thetimeinwhichaprojectisreadyforoccupancybytheownerisofconsiderableinterest
• Decisionswillbemadebasedontheanticipateddeliverydateofthecompletedproject
• Ownersoftenindependentlymonitorprojectstoevaluateadherencewiththeschedule
Someownerspreparethescheduleandhavethecontractorsmakesuggestionsfor
modificationsItismoretypicalforthecontractortopreparethescheduleforthe
owner’sapproval
TimeinContractProvisions
ProgressSchedule• Thecontractmaydictatethelevelofdetailtobeembodiedintheschedule
• Constraintsmayextendtotheamounttobepaidtothecontractorforeachactivity
• AprovisionmayspecificallyrequireuseofCPM,andacomputerbeusedtoperformcomputations
• Insomecases,receiptofaprogresspaymentmaybejeopardizedbyfailingtosubmitasatisfactoryscheduleortoproperlyupdatetheschedule
ProgressSchedule• Somecontractsstipulatethatupdatingofthescheduleshouldoccurmonthly
• Otherprovisionsaddress• Short-intervalschedules• Changesinworkactivitiesthatrequireadditionalstaff• Changesthatwillimpactinspectionrequirements
• MostU.S.governmentcontractsrestrictfloat-relatedprovisionstothefloatasdeterminedfromthecontractor’sschedule
NoticetoProceed• Thenoticetoproceeddocumenttypicallymarksthebeginningoftheactualconstructionduration
• Thecontractmustbeawarded—andsignedbybothparties—beforenoticetoproceedisissued
TimeofCompletion• Contractdurationistypicallystatedintermsofthetotalnumberofworkingdays• Ortotalnumberofcalendardaysallottedforcompletion
• Sometimes,specifiedcompletiondatesaregiven• Somecontractsstatethatcountingwillbeginonthedatespecifiedinthenoticetoproceed• Oragivennumberofdaysafterthenoticeisreceived
UnitsofTime:WorkingDaysorCalendarDays• Considerationmustbegiventotheunitsoftimeused—typicalconstructionschedulesusedays
• Ifthescheduleisconceptualinnature,durationsmightbestatedinweeks,months,orevenyears
Inturnaroundwork,whereacontractormakesmodificationstoafacilitywhilenormaloperations
areshutdownforashortperiod,durationsmightbesetintermsofshifts—orevenhours
TimeinContractProvisions
UnitsofTime:WorkingDaysorCalendarDays• Thereisabigdifferencebetweenworkingdaysandcalendardays
• Workingdaysmaybemorebroadlydefinedtoexcludeweekends,holidays—anddaysonwhichnoworkcanbeperformed
• Whatconstitutesadayonwhichnoworkcanbeperformedshouldbeclearlyaddressedpriortoenteringtheconstructioncontract
UnitsofTime:WorkingDaysorCalendarDays• Ifaprojectisweather-vulnerableorifweathercandramaticallyimpactworkprogress,schedulingwithworkingdaysismostcommon
• Projectsnotassusceptibletoadverseweatheraregenerallyscheduledintermsofcalendardays
• Publicownerstendtouseworkingdays,whileprivateownerstendtousecalendardays
Projectdurationsmaybedefinedbyaspecificcompletiondateinwhichsubstantial
projectcompletionislinkedtoaspecificcalendarormilestonedate
TimeinContractProvisions
UnitsofTime:WorkingDaysorCalendarDays• Whencompletiondatesareestablishedinthecontract,ownerstendtobereluctanttogranttimeextensionsfordelays
• Whenworkingdaysareused,contractualdurationgenerallyincludesallowancefordelaysresultingfromnormallyanticipatedweather
• Manycontractsdonotdefine“normallyanticipatedweather”• Referencemaybemadetolocalclimatologicaldata
Useofliquidateddamagesprovisionsinconstructioncontractsiscommon:“Damagesforavoidabledelayassetforthinthiscontractshallbeintheamountof___$perday”
DamagesforLateCompletion
DamagesforLateCompletion• Someprovisionsstatethecontractorwillbeliablefortheactualdamagesincurredbytheowner• Thistypeofprovisionwilllikelyresultinmorelitigation
• Aprovisionmayshowthattheownernotonlyacknowledgesthis—butthatthecontractorisnottocompromiseperformanceasaconsequenceofadverseweather
UseofCompletedPortionsoftheWork• Someprojectsareundertakeninoperatingfacilitiesinwhichtheownerortheowner’semployeeswillhaveacontinuingpresence
• Inotherprojectstheownermaywishtobeginusingportionsofaprojectthathavebeencompleted
• Ifsuchuseisanticipated,aspecificcontractualprovisiontothateffectisrequired
• Thecontractormustanticipatetheimpactsuchuseoroccupancywillhaveonconstructionoperations
SubstantialCompletion• Projectdurationistypicallymarkedorendedwiththesubstantialcompletionofaproject
• Aprojectisconsideredsubstantiallycompletewhentheownercanbegintooccupyandutilizethefacilityforitsintendedpurpose
• Theonlycontractortasksthatremainontheprojectitselfconsistofaddressingthepunchlistitems
Delays• Itisimportanttodefinethoseconditionsunderwhichthedurationmightbeextended• Relevantparticularlyintheareaofdelays
• Timeextensionsaretypicallygrantedforunavoidabledelays• Acontractormustcarefullydocumentinformationrelatedtodelays—andrequestextensionsinaccordancewiththecontractprovisions
Delays• Whileanextensionmaybegranted,thecontractormaybeaskedtopayforanyaddedcoststhattheownermayincurasaresultofthetimeextension
• Unavoidabledelaystypicallyhavealess-adverseimpactonthecontractor• Timeextensionsareoftenautomatic—whencertainproceduresarefollowed
• Theseprovisionsmustbecarefullyevaluatedtodeterminetheextentthatriskisplacedonthecontractor
Manycausesarefortimeextensionsonly,andthedelaydoesnotgiveanygrounds
forthecontractortoclaimfordamagesoradditionalcosts,expenses,overhead,profit,or
othercompensation
Delays
Submittals• Submittalsconstituteamajorcomponentoftheprocurementofmaterialsandequipment• Mayalsoberequiredonotheritems
• Withoutproperapprovalofsubmittalsonmaterials,thecontractorshoulddeferdeliveryofsuchitems
• Contractorsshouldpreparedocumentsforsubmittalearlyintheproject
ProgressPayments• Itiscommonforpaymentsintheconstructionindustrytobemadeonaperiodicbasis• Mostcommonlyonamonthlybasis
• Thisalleviatesfinancialhardshipthecontractorwouldassumeifpaymentwasnotmadeuntilprojectcompletion
• Paymentconditionsmustbecarefullyestablishedinordertoavoidanymisunderstandings
ProgressPayments• Mostownerspreferpaymentrequeststhatbearareasonablecomparisontothetruevalueofworkputinplace
• Whileacontractormaystillwishtofront-loadbillingstosomedegree,contractprovisionsoftensendaclearnoticetoavoidthispractice
• Theperiodicpaymentprovisionmayaddressthepaymentofmaterialsdeliveredbutnotinstalled• Somedocumentsaddressthisasaseparateissue
Thefinalpaymentistypicallyconsideredthepaymentconsistingofthereleaseofallofthewithheldretainage
FinalPayment
FinalPayment• Thelastperiodicpaymentwillprobablyprecedethefinalpaymentbyaconsiderableduration
• Ifthetimingofthefinalpaymentisclearlyoutlined,thecontractorcanmoreaccuratelypredictprojectcash-flowrequirements
Suspension• Foravarietyofreasons,anownermayfinditnecessarytohaltworkonaconstructionproject
• Actualreasonsmaynotbeanticipatedwhenthecontractdocumentsaredrafted
• Theownerwilltypicallywanttoincludeabroadprovisionthatpreservestherightofauthorizingasuspensioninthework
• Suspensionprovisionsmayonlygrantequitabletimeextensionstothecontractor—ortheymayalsostipulatecompensationtothecontractor
TerminationbyContractor• Projectterminationisaharshrealitythatacontractoroccasionallyfaces
• Whilearemotepossibilitywhenaprojectisbeingbid,thecontractorshouldreviewtheprovisionsrelatedtotermination
• Inparticular,thecontractormaywishtoevaluatetheconditionsunderwhichhe/shecanterminateacontract
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