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Project Management: A Managerial ApproachChapter 8 Scheduling1OverviewWBS to Schedule ProcessPERTSchedule TypesCPM

SchedulingA schedule is the conversion of a project action plan into an operating timetableIt serves as the basis for monitoring and controlling project activityTaken together with the plan and budget, it is probably the major tool for the management of projectsSchedulingIn a project environment, the scheduling function is more important than it would be in an ongoing operation Projects lack the continuity of day-to-day operations and often present much more complex problems of coordinationSchedulingThe basic approach of all scheduling techniques is to form a network of activity and event relationshipsThis network should graphically portray the sequential relations between the tasks in a projectTasks that must precede or follow other tasks are then clearly identified, in time as well as functionSchedulingSuch networks are a powerful tool for planning and controlling a project and have the following benefits:It is a consistent framework for planning, scheduling, monitoring, and controlling the projectIt illustrates the interdependence of all tasks, work packages, and work elementsIt denotes the times when specific individuals must be available for work on a given taskSchedulingNetwork benefits (cont.):It aids in ensuring that the proper communications take place between departments and functionsIt determines an expected project completion dateIt identifies so-called critical activities that, if delayed, will delay the project completion timeIt identifies activities with slack that can be delayed for specific periods without penaltySchedulingNetwork benefits (cont.):It determines the dates on which tasks may be started - or must be started if the project is to stay on scheduleIt illustrates which tasks must be coordinated to avoid resource timing conflictsIt illustrates which tasks may run, or must be run, in parallel to achieve the predetermined project completion dateIt relieves some interpersonal conflict by clearly showing task dependenciesA Process for Scheduling1. Think2. List activities3. Arrange activities considering precedence and relationships4. Develop Gantt charts and PERT/CPM networks5. Determine critical activities/critical path6. Crash and adjust as necessarySimple Schedule Gantt Chart

Gantt ChartsAdvantagesEasy to understandEasy to show progress and statusEasy to maintainMost popular view to communicate project status to client and/or senior managementDisadvantagesCan be superficialNot always easy to see precedence, relationshipsJANFEBMAR1815222951219265121926Network Techniques: PERT and CPMWith the exception of Gantt charts, the most common approach to scheduling is the use of network techniques such as PERT and CPMThe Program Evaluation and Review Technique (PERT) was developed by the U.S. Navy in 1958The Critical Path Method (CPM) was developed by DuPont, Inc during the same time periodNetwork Techniques: PERT and CPMPERT has been primarily used for research and development projects (Probalistic time)CPM was designed for construction projects and has been generally embraced by the construction industry (Deterministic time)The two methods are quite similar and are often combined for educational presentationScheduling TerminologyActivity - A specific task or set of tasks that are required by the project, use up resources, and take time to completeEvent - The result of completing one or more activities. An identifiable end state occurring at a particular time. Events use no resources.Network - The combination of all activities and events define the project and the activity precedence relationships

Scheduling TerminologyPath - The series of connected activities (or intermediate events) between any two events in a networkCritical - Activities, events, or paths which, if delayed, will delay the completion of the project. A projects critical path is understood to mean that sequence of critical activities that connect the projects start event to its finish event16Scheduling Terminology Merge Activity An activity that has more than one activity immediately preceding it (more than one dependency arrow flowing to it)Burst Activity Activity that has more than one activity immediately following it (more than one dependency arrow flowing from it)Parallel Activity Activities that can take place at the same time Scheduling TerminologyAn activity can be in any of these conditions:It may have a successor(s) but no predecessor(s) - starts a networkIt may have a predecessor(s) but no successor(s) - ends a networkIt may have both predecessor(s) and successor(s) - in the middle of a networkInterconnections from horizontal links in vertical WBSActivity on Arrow (1)8079Install softwareEventActivityStartContinueFinishActivity on Arrow (2)45132AApplicationapprovalDServiceavailabilitycheckCTrafficstudyBConstructionplans

Activity on Node XYZY and Z are preceded by XY and Z can begin at thesame time, if you wish(B)ABA is preceded by nothingB is preceded by AC is preceded by B(A)JKLMJ, K, & L can all begin atthe same time, if you wish(they need not occursimultaneously)All (J, K, L) must becompleted before M canbeginbutXZAAY(C)(D)Z is preceded by X and YAA is preceded by X and YCNetwork Exercise ActivityPredecessorANoneBNoneCADAEBFBGC,D,E,FDraw the project network with the following dataActivityPredecessorA-B-CADA,BEA,BFCGD,FHE,GRoll up Network PlanWP-2ABCDEFWP-1WP-4WP-3Level 1 - Milestone PlanLevel 2 - PlansLevel 3 - PlansBasic Scheduling Computation (1)Computation Nomenclature:Dij= Duration time for activity (i-j)Ei = Earliest occurrence time for event iLi = Latest allowable occurrence time for event IESij = Earliest start time for activity (i-j)EFij = Earliest finish for activity (i-j)LSij = Latest allowable start time for activity (i-j)LFij = Latest allowable finish time for activity (i-j)Sij = Total slack or float time for activity (i-j)FSij= Free slack (or float) time for activity (i-j)Ts= Scheduled time for the completion of a project or the occurrence of certain key events in a project

Basic Scheduling Computation (2)Forward Pass Computation

Rule 1: The initial project event is assumed to occur at time zeroE1 = 0

Rule 2: All activities are assumed to start as soon as possible, that is as soon as their predecessor activities are completedESij = Maximum of EF of preceeding activities

Rule 3: The early finish time of an activity is the sum of its early start time and the estimated activity durationEFij = ESij + DijBasic Scheduling Computation (3)Backward Pass Computation

Rule 1: The latest allowable finish time for the project terminal event (t) is set equal to either an arbitrary scheduled completion time for the project, Ts, or else equal to its earliest occurrence time computed in the forward pass computation.Lt=Ts or EtRule 2: The latest allowable finish time for an arbitrary activity (i-j) is equal to the smallest , or earliest, of the latest allowable start time of its successor activities.LFij = Minimum of LS of succeeding activitiesRule 3: The latest allowable start time for an arbitrary activity (i-j) is its latest allowable finish time minus the estimated activity duration time LSij = LFij - DijBasic Scheduling Computation (4)Total (Activity) SlackTotal activity slack is equal to the difference between the earliest and latest allowable start or finish times for the activity in question. For activity (i-j), the total slack is:Sij = LSij ESij or LFij EFijTotal slack represents the maximum allowable delay that can occur for non critical activities without delaying the project completion time. Once this slack is used up, noncritical activities become critical and any further delays will extend the project completion time.(Activity) Free SlackIs equal to the earliest start time of the successor activity(s) minus the earliest finish time of the activity in question.FSij = ESjk - EFij Free slack is the amount of time an activity can be delayed without affecting the start times of any successor activities.

Scheduling Exercise (1)

The following project represents a new business center that is toBe developed and the work and services the county engineering design department must provide as it coordinates with other groups such as the business center owners and contractors

Source: Gray & Larson, 2000Scheduling Exercise (2)ActivityPredecessorOptimisticMost LikelyPessimistic1. Lay foundationNone810132. Dig hole for scaleNone5683. Insert scale bases21315214. Erect frame1,31012145. Complete building41120306. Insert scales54587. Insert display cases52348. Put in office equipment746109. Finishing touches8,6234A company is expanding its operation to include a new drive-in weigh station. The station will be a heated/air condition building with a large floor and small office. The large room will have the scales, a counter and several display cases for its equipment. With the following data draw the network, project time and find the critical path, slack and Gantt ChartPrecedence Diagramming Method (1)The network scheduling procedure so far assumed a strict sequential relationship where the start of an activity is predicated upon the completion of its immediate predecessor, usually called Finish-to-Start (FS) relationship.The PDM allows other relationships such as start-to-start, finish-to-finish, start-to-finish, and also allows for time lags in the relationshipsPrecedence Diagramming Method (2)Trench1/3Trench1/3Trench1/3Lay pipe1/3Lay pipe1/3Lay pipe1/3Refill1/3Refill1/3Refill1/3Finish to Start with ladderingPrecedence Diagramming Method (3)XYLag 2Finish to Start with LagActivityMActivityNActivityPActivityQLag 5ABStart to StartPrecedence Diagramming Method (4)Trench1 mileLay pipe1 mileLag 3Refill1 mileLag 3Use of Lags to Reduce DetailsPrecedence Diagramming Method (5)Lag 4PrototypeTestingLag 3SystemdocumentationTestingFinish to Finish RelationshipStart to Finish RelationshipPrecedence Diagramming Method (5)Lag 2CodeDebugLag 4Combination RelationshipPERT/CPM Network ChartsAdvantagesAllows visualization of task relationshipsFacilitates calculation of critical pathClarifies impact of decisions on downstream activitiesDisadvantagesComplex, not easy to comprehend at a glanceCharts dont readily depict durations, dates, progressHypothetical Network2561435166201330TE=64Calculate t(e) and Z for this networkActivity and Project Frequency Distributions

ACTIVITYPROJECTambTE(A)(B)PERT Activity Calculationt(e) = a + 4m + ba = Most Optimistic (MO) 6m = Most Likely (ML)b = Most Pessimistic (MP)t(e) = Activity DurationWhen a single estimate for activity time is not sufficient!PERT Schedule ProbabilityZ is derived from a table of predetermined probabilitiesZ = T(S) T(E)Z = Probability of SSD(T[E])2 Meeting Schedule

T(S) = Scheduled Duration

T(E) = Critical Path DurationPERT Activity Times & VariancesActivityambt(e)1-21729472-3612242-41619283-51316194-525145-6258Variance of Activity EstimatesActivityambt(e)[(b-a)/6]2Var1-2172947302-361224132-4161928203-5131619164-5251465-62586Possible Project Durations

TE=64TS=67Z TableZ ValueProbabilityZ ValueProbability-2.00.02+2.00.98-1.50.07+1.50.93-1.00.16+1.00.84-0.70.24+0.70.76-0.50.31+0.50.69-0.30.38+0.30.62-0.10.36+0.10.54

Z-Table ExpandedGantt ChartsThe Gantt chart shows planned and actual progress for a number of tasks displayed against a horizontal time scaleIt is an effective and easy-to-read method of indicating the actual current status for each set of tasks compared to the planned progress for each item of the setIt can be helpful in expediting, sequencing, and reallocating resources among tasksGantt charts usually do not show technical dependenciesGantt ChartsThere are several advantages to the use of Gantt charts:Even though they may contain a great deal of information, they are easily understoodWhile they may require frequent updating, they are easy to maintain Gantt charts provide a clear picture of the current state of a projectThey are easy to constructDrawing NetworksActivity-on-Arrow (AOA) networks use arrows to represent activities while nodes stand for eventsActivity-on-Node (AON) networks use nodes to represent activities with arrows to show precedence relationshipsThe choice between AOA and AON representation is largely a matter of personal preferencePartial AOA Network2314AXCBE(A)2314ABCXE(B)2314ABXCE(C)Full AOA NetworkKOLL BUSINESS CENTERCounty Engineers Design Department2314A5BC10X51506780YF10G170H35E15D5ActivityDurationLegendExample

Consider the following project (times in days)ActivityambPredecessora147-b222-c258ad345ae468c,bf006c,bg369d,eFind:The networkExpected activity time, variances and slackThe critical path and expected completion timeThe probability the project will be done in 23 daysThe completion time corresponding to 95% probability.ActivityambTEa1474b2222c2585d3454e4686f0061g3696ActivityambTEVariancesa14741b22220c25851d34540.11e46860.44f00611g36961SELESAI1

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