Class 3: Project Scheduling II

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1 Engineering Management 1 Class 3: Project Scheduling II Ruel Ellis Department of Mechanical and Manufacturing Engineering P r ecedence Diagr amming Met hod P r oj ect R es our ces : L oading P r oj ect R es our ces L eveling P r oj ect S chedule Compr es s ion

2 P r ecedence Diagr amming Met hod (PDM) Precedence Diagr amming Method Extension of basic PE R T /CPM Permits partial parallel performance of mutually dependent activities llowance of overlap of activities - not just serial Better recognition of real world relationships between activities

3 Precedence Diagr amming Method Used by virtually all pr oj ect management software More popular than CPM/PERT method llows more flex ibility than CPM/PERT in lead/lag r elations hips different types of dependencies P DM L ead-l ag R elat ions hips

4 P DM ctivity R elat ions hips Complements traditional PERT (S tart-finish) relationship between activities Four additional lead-lag relationships besides simple S tart -to- S tart lead SS B Finish -to- Finish lead FF B Finish -to- S tart lead FS B S tart -to- Finish lead S F B P DM S tart to S tart S tart -to- S tart lead SS B ctivity B cannot start until activity has been in progres s for at least SS time units SS B = 2 B

5 P DM Finish to Finish Finish -to- Finish lead FF B ctivity B cannot finish until at least FF time units after completion of activity B FF B = 4 P DM Finish to S tart Finish -to- S tart lead FS B ctivity B cannot start until at least FS time units after the completion of activity FS B = 3 B

6 P DM S tart to Finish S tart -to- Finish lead S F B there mus t be at least SF time units between the start of activity and the completion of activity B SF B = 6 B Problem Exercise:PERT Net w or k nalysis Complete the PERT network ON diagram for the pr oj ect. You want to deter mine Critical Path Duration of the Cr itical Path

7 E xample Project c tivity D e s c riptio n P re d D ur "a" D ur "m" D ur "b" (da ys ) (da ys ) (da ys ) Test Plan Design N one B Prototype Sample Const C Shock Testing B D Environmental Testing B E Shock Test nalysis B,C F Shock Test Report E G Final Testing Draft Report D,F H Final Test Report Delivery F,G E xample Project (b-a)/6 (a + 4m + b)/6 c tivity D e s c riptio n P re d D ur "a" D ur "m" D ur "b" T e S td (da ys ) (da ys ) (da ys ) (da ys ) D e v Test Plan Design N one B Prototype Sample Const C Shock Testing B D Environmental Testing B E Shock Test nalysis B,C F Shock Test Report E G Final Testing Draft Report D,F H Final Test Report Delivery F,G

8 P E R T Network nalysis What is the pr obability that the pr oj ect will complete in Less than 54 days? Greater than 54 days? Greater than 57 days? Less than 48 days? 95% confidence r ange for duration? Constrained R es our ces

9 Resource llocation - the Issue I ssues of resource utilization and availability fact of life S cheduling is focused on time physical resources are also impor tant Resources (including time) must be cons ider ed example, the students workload Project Constraints: Principal Types T echnical constraints T ask inter-relationships Resource Cons tr aints People Mater ials Equipment Capital Physical constraints

10 Resource Constraining CPM & PERT both assume unlimited r es our ces NOT TRUE may have only a finite number of skilled assets (example - s ystems analysts, programmers) R E S OU R CE LEVELING - balance the r es our ce load R E S OU R CE CONSTRINING - don t exceed available r es our ces Constrained Resources Constrained r es our ce pr oblem activity, duration, and r es our ces S UBJECT TO (fill in the blank) Generally accepted appr oaches : Heuristic Methods (rules of thumb) used by software for leveling resources Optimization Models (mathematical) not good for large complex situations

11 R es our ce L oading Resource Loading Project Manager is responsible for the des ign which will: Provide r equired r es our ces, in the r equired amounts, to where they are needed, when they are needed Loading pr ovides a pictur e of the work flow requirements in a proj ect throughout the pr oj ect life cycle

12 Resource Loading T ime-phased r es our ces - describes amount of individual resources an existing s chedule r equires during specific time per iods Resource loads (requirements) of each resource type ar e listed as a function of time per iod T he schedule becomes directly linked to requirements for s upporting resources Resource Loading R es our ce loading is the time individual resources (people, subcontractors, groups) have committed to a pr oj ect I ntroduction of constraints to the schedule

13 Resource Loading Constraints to the s chedule Can be given as a per centage Can provide dates of availability Work contour loading couple of issues: Overloading Pay overtime, Work over Underloading 100% committed (wasted r es our ce) R es our ce L eveling

14 Resource Leveling Based on the r es ults from the resource loading identification of peaks and valleys in resources assigned to the pr oj ect Leveling is designed to cr eate a smoother distribution of resource usage reduce var iability of resource commitment Leveling also changes cost (cash flow) distribution Resource Leveling R es our ce leveling is the pr ocess of shifting r es our ce us age to dis tr ibute workload of team members and availability of equipment/critical resources T his is where the pr oj ect managers earn their money making s chedulecosts tradeoffs

15 Resource Leveling ppr oaches to r es our ce leveling Redistribution of work split/stagger activities T ask shifting using s lack as shifting lever age dd additional resources S ubstitute r es our ces (temporary) Change s cope Eliminate activities Change s chedule Resource Leveling Example: Unleveled 1st Qtr 2nd Qtr 3rd Qtr 4th Qtr an alysts programmers train ers

16 25 Resource Leveling Example: Leveled analysts programmers train ers 0 1st Qtr 2nd Qtr 3rd Qtr 4th Qtr Resources and Scheduling R es our ce leveling ssumes s ufficient resources to meet peak project demands S chedule tas ks to s mooth or balance use of resources R es our ce constr ained scheduling ssumes ins ufficient resources to meet peak project demands S chedule tas ks to minimize pr oj ect duration while adher ing to limited resources

17 Resources and Scheduling ssumptions (for convenience not in practice) T asks cannot be pr e-empted Constant resource level requirement for each task Resource Leveling: n Illustrative Example B C E F G D

18 Task Schedule Details: CPM at Work Task Resources DUR ES EF LS LF SL B C D E F G Which are the cr itical tasks? Will now level use of resources: assume only 1 type of resource us ed. Leveling Tas k Res DUR ES LF S L B C D E F G Tota l

19 Leveling Tas k Res DUR S L B C D E F G Total Leveling Re source s S eries

20 Leveling Tas k R e s D UR S L B X X C D E F G total Leveling Resources S eries 1

21 MS Project (automatic leveling factors) 1. Predecessor delay tasks without dependencies first 2. Total slack delay tasks with more slack 3. Start Date delay tasks that start earlier 4. Priority Value delay lower priority tasks first 5. Constraints constrained tasks less likely to be delayed P r oj ect S chedule Compr ession

22 S hor t Exercise: S hor t ening the S chedule I dentify several possible r eas ons why we might want to shorten the dur ation for a pr oj ect. S hor t ening the Project Duration Why would we want to s hor ten the duration of a pr oj ect? Changed pr ogr am deadlines Change in project scope or technical performance r equir ements Budget timing s hifts S hift in Resources M 5 I How can you shorten the pr oj ect duration? -- T ypical pproaches

23 S hor t ening the Project Duration Descope or decontenting T echnical performance r elief or reduction S acr ifice quality S ubcontract elements I ntroduce differ ent appr oach/technology (risk?) ssign additional resources I ncrease utilization of current resources Rearrange s equencing of tasks S hor t ening a Project S chedule S hortening dur ations of critical tasks usually requires : (1) adding mor e resources, (2) changing the s cope, and/or (3) changing the s equencing S chedule cr ashing - obtaining the greatest amount of schedule compression for the leas t incremental cost F as t tracking parallel processing activities or overlapping them

24 S chedule Compr ession: Cr as hing a Project Crashing as a pr oblem vs. crashing as an exercise Why is this so difficult? Proj ect system I ntended and unintended cons equences Crashing by design vs. crashing by force Example, rebuilding the interstate Cr as hing a P r oj ect Recognize a r elations hip between proj ect cost and s chedule Provides the pr oj ect manager information to make inf or med decis ions about tradeoff of time for cost, or vice ver s a S pecify (normal time, crash time) and (nor mal cost, crash cost)

25 Cr as hing S equence 1. Determine cr itical path 2. Establish cost slope for each activity on the cr itical path 3. S elect activity with lowest cost slope decrease by unit 4. Recompute new time, cost, and critical path 5. Repeat steps 2-4 until the desired dur ation is achieved Cos t Slope cost slope = C T C = crash cost C C = normal cost n T = crash time c T = normal time n c c C T n n

26 Cr as hing Example P r oblem ctivity Predecessor Duration B C D* E** -- B S hor t Exercise: Project S chedule Cr ashing Draw an activity on arc diagram for the pr oj ect. Determine the cr itical path and the dur ation for the cr itical path.

27 ct B C D* E** Cr as hing Example P r oblem Pred -- B,C B Dur Normal Dur Crash Cost ($) Normal * partial crashing per mitted ** no par tial crashing per mitted Cost ($) Crash Cost Slope $/wk (2 wks) S hor t Exercise: Project S chedule Cr ashing Determine the cos t slope for each activity in the proj ect and s elect the activity to cr as h to reduce the pr oj ect by 1 week.

28 ct B C D* E** Cr as hing Example P r oblem Pred -- B,C B Dur Normal Dur Crash Cost ($) Normal * partial crashing per mitted ** no par tial crashing per mitted Cost ($) Crash Cost Slope $/wk (2 wks) Cr as hing L imit at ions ssumes linear relationship between time and cos t Not usually true (indir ect costs don t change at same r ate as direct costs) Requires a lot of extra cos t es timation T ime cons uming Ends with tradeoff decision something has to give C, P, T, or S

29 P r oj ect S chedule F ast T r acking F as t -T r acking different approach to pr oj ect schedule compr ession Overlapping the activity sequencing example concurrent engineering EXMPLE (Factory of the Futur e) What are s ome of the issues in Fast-tracking?

30 S hor t ening Project S chedules Original schedule Shortened duration Overlapped tasks I ssues in P r oj ect S cheduling

31 S cheduling I ssues Busting the cr itical path Critical Path MI S CONCEPT I ONS : T he cr itical path defines all the critical project activities; this is all that is critical for the PM T here is one cr itical path for a proj ect T he cr itical path is a cons tant once es tablished for a pr oj ect S cheduling I ssues I mportance of estimating S chedule tr ade-offs ---- Cost = f(performance, Scope, T ime) S cheduling is only part of a complete appr oach to pr oj ect management T radeoffs between sophistication and cos t of methods for scheduling estimation & analys is

32 S cheduling I ssues Proj ect scheduling is critical Proj ect duration typically a primary focus S chedule s lippage linked to: I ncreased cos ts Unhappy customers Unhappy management S cheduling I ssues Proj ect scheduling difficult (developing pr ecedence relationships, task durations) Most PMs do not perform pr obabilis tic analys is Most new DoD and other major procurements require pr oj ect schedule r isk analysis

33 Next Class Session Estimation of Project Costs Project Control Earned Value nalysis Monitoring Project Progress

Lecture 2: Project Scheduling I

Engineering Management 1 Lecture 2: Project Scheduling I Ruel Ellis Department of Mechanical and Manufacturing Engineering Network Scheduling Critical Path Method Program Evaluation & Review Technique