CPMPERT Critical Path Method Project Evaluation Review Technique
- Slides: 28
CPM/PERT Critical Path Method Project Evaluation Review Technique Pongsa Pornchaiwiseskul, Faculty of Economics, Chulalongkorn University 1
CPM/PERT Tools for Project Management – Minimum Project Duration – Scheduling – Time-cost Trade-offs – Resoruce Leveling (not to be discussed( Pongsa Pornchaiwiseskul, Faculty of Economics, Chulalongkorn University 2
Critical Path Method • Network-based (to be seen why ( • An LP Problem but much more simple that it can be solved by hand • Deterministic (all the parameters are known or assumed with certainty( Pongsa Pornchaiwiseskul, Faculty of Economics, Chulalongkorn University 3
Project Evaluation Review Technique • Extension of CPM • Probability Concept is added to CPM • Good for a project which has never been done before. Some uncertainty involved Pongsa Pornchaiwiseskul, Faculty of Economics, Chulalongkorn University 4
PROJECTS • There are many activities. Each activity takes time. • Some activities (successors) cannot start until the other activities (predecessors) finish. • Can be represented by a directed network • Examples are construction, scientific project and thesis Pongsa Pornchaiwiseskul, Faculty of Economics, Chulalongkorn University 5
Activity-on-Node (Ao. N( Act. A Act. B Act. C Act. D Pongsa Pornchaiwiseskul, Faculty of Economics, Chulalongkorn University 6
Activity-on-Arc (Ao. A( activity A S activity B F activity C activity D Pongsa Pornchaiwiseskul, Faculty of Economics, Chulalongkorn University 7
EXAMPLE OF CPM Activity DIG FOUND POURB JOISTS WALLS RAFTERS FLOOR ROUGH ROOF FINISH SCAPE Time 34 2 3 5 3 4 6 7 5 2 Predecessors DIG FOUND WALLS, POURB JOISTS FLOOR RAFTERS, JOISTS ROUGH, ROOF POURB, WALLS Pongsa Pornchaiwiseskul, Faculty of Economics, Chulalongkorn University 8
MINIMUM PROJECT DURATION • Network Method – by hand – by computer programs, e. g. , Microsoft Project (not to be discussed( • Solving its corresponding LP problem – by computer or by hand Pongsa Pornchaiwiseskul, Faculty of Economics, Chulalongkorn University 9
Network Method by Hand • Determine Longest route between start and end • Performed in two steps. – Forward Pass(from start to end( – Backward Pass (from end back to start( Pongsa Pornchaiwiseskul, Faculty of Economics, Chulalongkorn University 10
FORWARD PASS (1)The project starts at time zero (2)Every starting activity has an Earliest Start(ES) at zero (3)Earliest Finish(EF) of an activity is ES + activity time EFj = ESj + Dj (4)For an activity j w/ predecessors, ESj = max{ its predecessors’ EF { Pongsa Pornchaiwiseskul, Faculty of Economics, Chulalongkorn University 11
FORWARD PASS (cont’d( (5)The minimum project duration (T( T = max{EF of activities w/o successors{ Note that (1 The project can earliest finish at time T (2 It can finish later than time T but not before Pongsa Pornchaiwiseskul, Faculty of Economics, Chulalongkorn University 12
BACKWARD PASS (1)The project finishes at time T (2)All the activities w/o successors can Latest Finish(LF) at time T. Their LF = T (3)Latest Start(LS) of an activity j is its LF minus activity duration (D), I. e, . LSj = LFj - Dj (4)LF of an activity w/ successors = min {LS of its successors{ Pongsa Pornchaiwiseskul, Faculty of Economics, Chulalongkorn University 13
Ao. N Representation DIG(3( FOUND(4( JOISTS(3( FLOOR(4( ROUGH(6( POURB(2( RAFTERS(3( ROOF(7( WALLS(5( SCAPE(2( Pongsa Pornchaiwiseskul, Faculty of Economics, Chulalongkorn University FINISH(5( 14
AON Legend ES EF ACTIVITY (D( LS LF Pongsa Pornchaiwiseskul, Faculty of Economics, Chulalongkorn University 15
Ao. N Representation 1420 JOISTS(3( 10 14 FLOOR(4( ROUGH(6( 7 9 1215 1522 22 27 ROOF(7( FINISH(5( 7 10 9 12 0 3 DIG(3( 0 3 3 7 FOUND(4( 3 7 12 16 POURB(2( RAFTERS(3( 7 12 1214 10 12 WALLS(5( 7 12 1215 16 22 15 22 2227 SCAPE(2( 2527 Pongsa Pornchaiwiseskul, Faculty of Economics, Chulalongkorn University 16
Ao. A Representation 3 WA LLS 5 RB I 3 FTERS 2 G POU RA FOUND B C 4 ROUGH H 6 RO OF 7 0 JOI S DIG A 3 F SIH FIN 5 TS D FLOOR 4 E SCAPE 2 Pongsa Pornchaiwiseskul, Faculty of Economics, Chulalongkorn University 17
RESULT Activity DIG FOUND POURB JOISTS WALLS RAFTERS FLOOR ROUGH ROOF FINISH SCAPE Time Predecessors ES 3 0 4 DIG 3 2 FOUND 7 3 FOUND 7 5 FOUND 7 3 WALLS, POURB 12 4 JOISTS 10 6 FLOOR 14 7 RAFTERS, JOISTS 15 5 ROUGH, ROOF 22 2 POURB, WALLS 12 EF 3 7 9 10 12 15 14 20 22 27 14 Pongsa Pornchaiwiseskul, Faculty of Economics, Chulalongkorn University LS 0 3 10 10 7 12 12 16 15 22 25 LF 3 7 12 12 12 15 16 22 22 27 27 18
LP Representation MAX 3 DIG+4 FOUND+2 POURB+3 JOISTS+5 WALLS 3 RAFTERS+4 FLOOR+6 ROUGH+7 ROOF+5 FINISH+ 2 SCAPE+ SUBJECT TO (2 DIG <=1 (3 FOUND - DIG = 0 (4 JOISTS + POURB + WALLS - FOUND =0 Pongsa Pornchaiwiseskul, Faculty of Economics, Chulalongkorn University 19
LP Representation(cont’d( (5 FLOOR + DUMMY - JOISTS =0 (6 RAFTERS + SCAPE - POURB - WALLS = 0 (7 ROUGH - FLOOR = 0 (8 ROOF - RAFTERS - DUMMY = 0 (9 FINISH - ROUGH - ROOF = 0 END Pongsa Pornchaiwiseskul, Faculty of Economics, Chulalongkorn University 20
SCHEDULING WITH BAR CHART Activity 5 10 15 20 25 DIG FOUND POURB JOISTS WALLS RAFTERS FLOOR ROUGH ROOF FINISH SCAPE Pongsa Pornchaiwiseskul, Faculty of Economics, Chulalongkorn University 21
CRITICAL ACTIVITIES • activities with zero slack = LS -ES or = LF - EF • critical activities form a Critical Path Pongsa Pornchaiwiseskul, Faculty of Economics, Chulalongkorn University 22
TIME COST TRADE-OFFS Choose to shorten the critical activity with lowest cost until the activity becomes non-critical. Pongsa Pornchaiwiseskul, Faculty of Economics, Chulalongkorn University 23
CRASHING THE PROJECT Decrease the project duration by shortening the activities. Activity Normal Duration Max. Crash $/day DIG 3 1 50 JOIST 3 1 30 WALLS 5 3 40 FINISH 5 2 80 Pongsa Pornchaiwiseskul, Faculty of Economics, Chulalongkorn University 24
UNCERTAINTY Activity duration could be uncertain A - optimistic time estimate B - pessimistic time estimate M - most likely time estimate (mode( Pongsa Pornchaiwiseskul, Faculty of Economics, Chulalongkorn University 25
DURATION ESTIMATES A M B time Mean D = (A+4 M+B)/6 Standard Deviation SD = (B-A)/6 Pongsa Pornchaiwiseskul, Faculty of Economics, Chulalongkorn University 26
PERT Method • Do CPM using its Mean D for the duration of each activity • CPM yields the Mean project duration • The variance of project duration T Var(T) = sum of Var(D) for all the critical activities in a CP Pongsa Pornchaiwiseskul, Faculty of Economics, Chulalongkorn University 27
Activity DIG FOUND POURB JOISTS WALLS RAFTERS FLOOR ROUGH ROOF FINISH SCAPE RESULT Time Predecessors ES 34 DIG 2 FOUND 3 FOUND 5 FOUND 3 WALLS, POURB 4 JOISTS 6 FLOOR 7 RAFTERS, JOISTS 5 ROUGH, ROOF 2 POURB, WALLS EF Pongsa Pornchaiwiseskul, Faculty of Economics, Chulalongkorn University LS LF 28
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