Quản lí dự án - Chapter 6: Allocating resources to the project

Chapter 6Allocating Resources to the ProjectIntroductionProjects compete with each other for resourcesIf resource is used but not consumed, which project must wait to use resourceIf resource is consumed during use, may not be available for other projects or other projects must wait for replacementIn either case, one project must waitOne project is delayedLikewise, different activities on the same project may compete for resourcesTrade-offs must be madeExpediting a Project (Assumptions)Smaller problem to avoid unnecessary arithmeticProblem set in a deterministic worldAll estimates of task duration are based on normal (or standard) resource loadingsExpediting a Project (Approaches)The critical path methodFast-tracking a projectProject expediting in practiceOpportunities before the project beginsOpportunities when the project is underwayThe Critical Path MethodNormal duration estimatesNormal costsCrash duration estimatesCrash costsCrash cost per dayNotes on CrashingImportant to make sure the resources required to crash the project are availableTechnology may be used to crash an activityUsing Ditch Witch to dig a ditch rather than adding more workersMay have to expedite tasks not on critical path to make resources available to other projectsSome tasks cannot be crashedHow to CrashStart with the normal scheduleSelect activities to crash, one at a timeFocus on the critical path(s)Select least expensive activity to crashCalculate slope information on activities to crashAn Example of a Normal/Crash ProjectTable 6-1A PERT/CPM Example of Crashing a Project, AOA Network Part 1Figure 6-1 (Partial)A PERT/CPM Example of Crashing a Project, AOA Network Part 2Figure 6-1 (Partial)CPM Crash Cost-Duration HistoryFigure 6-2Fast-Tracking a ProjectAn expediting technique in which one phase of the project is started before preceding phases are completedUsed in the construction industry when the building phase is started before the design and planning phases are complete This technique is particularly appropriate when large proportion of work is routineProject Expediting in PracticeProject manager may know ahead of time that this project is time-critical and needs to be finished as early as possibleProject manager may during project that it needs to be finished earlierSomething delays the project and time needs to be made upOpportunities Before the Project BeginsMost projects have one time estimateMany projects have a project “buffer”A project time contingency may be added as wellCan monitor key activities closelyMay order long-lead time items earlyOpportunities When the Project Is UnderwayFocus on critical pathUse contingency timePull resources from less critical activitiesMove buffers to more critical activitiesMay skip less critical stepsMay postpone activities involving non-core membersMove activities to post-project phaseMay run activities in parallel or use weekendsPressuring team to work fasterGet additional resources for overtime or more peopleMay reduce scopeMay wait and seeResource LoadingRefers to the amounts of specific resources that are scheduled for use on specific activities or projects at specific timeIt is usually presented in the form of a list or tableWill see using short documentary DVD exampleProject Plan and Gantt Chart for Production of a Short Documentary FilmFigure 6-3Gantt Chart for DVD Project, Adjusted for Client AvailabilityFigure 6-4Resource Loading Chart for DVD ProductionTable 6-3Resource Loading IssuesMost project management software assumes that any resource assigned to an activity will work on that activity 100 percent of the time availableCan be resolved by allocating a specific percentage of time to projectIt is easy to over utilize human resourcesOvertime is expensiveResource LevelingTo perform resource leveling, software will move activities so that resources do not exceed their capacityUsing available slack firstExtending project duration where using slack does not workProject manager may not try to level all resourcesA working schedule may require more resourcesA more-or-less steady state demand for human resources is highly desirableResource Over Allocation Report for Scriptwriter Showing All ActivitiesFigure 6-5Graphic Resource Over Allocation Report for ScriptwriterFigure 6-6Resource Leveled Report for Scriptwriter Showing All ActivitiesFigure 6-7Graphic Resource Leveled Report for ScriptwriterFigure 6-8Daily Resource Loading Chart for Scriptwriter Leveled Table 6-4Final Gantt Chart Schedule, Scriptwriters and Producer LeveledFigure 6-9Resource Loading/Leveling and UncertaintyHolidays, vacations, sick days can reduce human resource availabilityNot all required facilities and equipment will be available when neededThere may be change ordersAll of these must be factored into plansAllocating Scarce Resources to ProjectsLeveling resources using slack is often not possibleSoftware needs instructions about what priority to use when allocating scare resourcesWhen demand exceeds supply, software assigns a resource according to some priority rule selected by project managerThe key problem is deciding which activities gets the scare resource and in what orderSome Priority RulesAs soon as possibleAs late as possibleShortest task duration firstMinimum slack firstMost critical followersMost successorsMost resources firstAllocating Scare Resources to Several ProjectsWhen the allocating scarce resources is extended to where several projects are being carried out concurrently, the size and complexity of the problem increaseHowever, the nature of the underlying problem remains the sameThere is a decided advantage if several projects are joined as a setWith several projects, we can link them together with pseudoactivitiesPseudoactivitiesPseudoactivities are those which have duration but require no resourcesThe use of pseudoactivities allows a set of projects to be linked and dealt with as though it were a single projectThe individual projects are interrelated by specifying predecessor/successor relationships in Microsoft ProjectThey appear to Project to be parts of one projectAllows use of Microsoft Project resource loading and leveling charts and tablesMultiple Projects Connected with PseudoactivitiesFigure 6-11Criteria of Priority RulesProject manager faces the problem of choosing between different outcomes that result from different priority rulesMust also deal with different arrangements and durations of pseudoactivitiesThere are many measurable criteria to help select a priority ruleSchedule slippage: amount project or set of projects delayed by application of a leveling rule Resource utilization: extent to which resources are over or underworkedIn-process inventory: amount of unfinished work in the systemThe Basic ApproachBasic approach is borrowed from a manufacturing modelThere is a set of activities for one or more projects to be processed by a limited number of resourcesNot all activities require the same resourcesSome activities have higher prioritiesSome activities need more work than othersSome activities must be done before othersActivity start times not known exactlyActivity processing times not know exactlyResource Allocation and the Project Life CycleScheduling method uses rule to assign scare resources to activitiesStarts with most urgent and works downProcess continues until no more activities qualityIf scarce resource is depleted before all non-critical activities are loaded, they go unsuppliedThey then become a higher priority in later periodsResource Allocation and the Project Life Cycle ContinuedWhat happens if scare resource is depleted before all critical activities are assignedMay borrow from another ongoing activity with slackMay even deschedule the activityCan use knowledge of the project’s life cycle to help make the decisionProject or Task Life CyclesFigure 6-12Goldratt’s Critical ChainProjects are completed faster when there are fewer of them struggling for attention from a limited set of facilitiesGoldratt’s focus in the Critical Chain is on a single project with multiple demands on a scarce resourceThe logic extends to the multiproject case without alterationResource usage and project schedules are inextricably bound togetherThe technological necessities that force schedules to be ordered in specific ways simultaneously force resources to be used in specific waysProject IssuesProject due dates are too often unrealisticThere are too many changes made in the project’s scopeKey resources and data are often unavailable when neededThe budget is frequently unrealistic and therefore often exceededIt seems like my project is always in competition for resources with other projectsCritical Chain ContinuedIt is not farfetched to conclude that the causes of these problems are generic to all types of projectsProblems encountered when managing projects are strongly related to the need to trade off one project objective for anotherTo what extent is the need to make these trade-offs are caused by human decisions and practicesIn other words, can more effective project management minimize the occurrence of these problems?Will examine the complaint regarding unrealistic due dates in more detailThree Project ScenariosFigure 6-13How Long?Each task takes 10 daysWhat is the completion time for each project?All three would have the same duration of 50 daysSimple project with five tasks takes the same time as complex one with 11 tasks!Part of ProblemPart of the problem is the assumption that the activity times are known with certaintyAssume all activities are normally distributedMean of 10Standard deviation of threeEach is simulated 200 timesProject Completion Time Statistics Based on SimulationTable 6-5AnalysisThis example clearly demonstrates how the commonly made assumption of known activity times in practice can lead to quite unrealistic project deadlinesThe results would have been even more dramatic had the activities required some common resourcesSimilarly, the results would have been more dramatic and realistic had a nonsymmetrical distribution been used to model the activity timesEstimating Task TimesWorkers often pad time estimatesInflated time estimates tend to create even more problemsWhen workers finish a padded activity early, they often do not let management know they are done yetWorse, workers may perceive they have plenty of time to complete the task and therefore delay starting the taskGoldratt refers to this as the student syndromeMultitaskingMultitasking is assigning team members to multiple projects and having them allocate their time across these projectsThere is typically a penalty or cost associated with switching from working on one project to anotherSample Project with MultitaskingFigure 6-16Alternative Gantt Charts for Projects A and BFigure 6-17Common Chain of EventsAssuming that activity times are known and that the paths are independent leads to underestimating the actual amount of time neededBecause the time is underestimated, project team members tend to inflate their time estimatesInflated time estimates lead to work filling available time, workers not reporting that a task has been completed earlyAn important caveat then becomes that safety time is usually visible to project workers and is often misusedMisused safety time results in missed deadlines and milestonesCommon Chain of Events ContinuedHidden safety time further complicates the task of prioritizing project activitiesThe lack of clear priorities likely results in poor multitaskingTask durations increase as a result of poor multitaskingUneven demand on resources may also occur as a result of poor multitaskingIn an effort to utilize all resources fully, more projects will be undertaken to make sure that no resources are underutilizedAdding more projects further increases poor multitaskingResolving These ProblemsGoldratt suggests that the key to resolving this is to schedule the start of new projects based on the availability of bottleneck resourcesHe further suggests that time buffers be created between the bottleneck resource and the resources that feed itHe also suggests reducing the amount of safety time added to individual tasks and then adding some fraction of the safety time reduced back into the system as safety buffer for the entire projectThe Critical ChainAnother limitation is the dependency between resources and tasks is often ignoredUsing traditional approaches, A1-C1 is the critical pathWhat if A1 and A2 are not independentThen page A1-C1 increases to 22 daysAddressing ProblemNeed to consider both precedence relationships and resource dependenciesGoldratt proposes thinking in terms of the longest chain of consecutively dependent tasks where such dependencies can ariseReferred to as critical chainThere are two potential sources that can delay the projectDelay in the tasks that make up the critical chainDelay in activity feeding the critical chain that results in delay of the critical chainProject and Feeder BuffersFigure 6-19CopyrightCopyright © 2014 John Wiley & Sons, Inc.All rights reserved. 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