Project Management: A Managerial Approach Chapter 8 – Scheduling

Overview WBS to Schedule Process PERT Schedule Types CPM

Scheduling A schedule is the conversion of a project action plan into an operating timetable It serves as the basis for monitoring and controlling project activity Taken together with the plan and budget, it is probably the major tool for the management of projects

Scheduling In 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 coordination

Scheduling The basic approach of all scheduling techniques is to form a network of activity and event relationships This network should graphically portray the sequential relations between the tasks in a project Tasks that must precede or follow other tasks are then clearly identified, in time as well as function

Scheduling Such 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 project It illustrates the interdependence of all tasks, work packages, and work elements It denotes the times when specific individuals must be available for work on a given task

Scheduling Network benefits (cont.): It aids in ensuring that the proper communications take place between departments and functions It determines an expected project completion date It identifies so-called critical activities that, if delayed, will delay the project completion time It identifies activities with slack that can be delayed for specific periods without penalty

Scheduling Network benefits (cont.): It determines the dates on which tasks may be started - or must be started if the project is to stay on schedule It illustrates which tasks must be coordinated to avoid resource timing conflicts It illustrates which tasks may run, or must be run, in parallel to achieve the predetermined project completion date It relieves some interpersonal conflict by clearly showing task dependencies

Simple Schedule – Gantt Chart

Network Techniques: PERT and CPM With the exception of Gantt charts, the most common approach to scheduling is the use of network techniques such as PERT and CPM The Program Evaluation and Review Technique (PERT) was developed by the U.S. Navy in 1958 The Critical Path Method (CPM) was developed by DuPont, Inc during the same time period

Network Techniques: PERT and CPM PERT has been primarily used for research and development projects CPM was designed for construction projects and has been generally embraced by the construction industry The two methods are quite similar and are often combined for educational presentation

Scheduling Terminology Activity - A specific task or set of tasks that are required by the project, use up resources, and take time to complete Event - 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 Terminology Path - The series of connected activities (or intermediate events) between any two events in a network Critical - Activities, events, or paths which, if delayed, will delay the completion of the project. A project’s critical path is understood to mean that sequence of critical activities that connect the project’s start event to its finish event

Scheduling Terminology An activity can be in any of these conditions: It may have a successor(s) but no predecessor(s) - starts a network It may have a predecessor(s) but no successor(s) - ends a network It may have both predecessor(s) and successor(s) - in the middle of a network Interconnections from horizontal links in vertical WBS

Hypothetical Network 2 5 6 1 4 3 16 20 13 30 TE=64 Calculate t(e) and Z for this network……

Activity and Project Frequency Distributions m b TE (A) (B)

PERT Activity Calculation t(e) = a + 4m + b a = Most Optimistic (MO) 6 m = Most Likely (ML) b = Most Pessimistic (MP) t(e) = Activity Duration When a single estimate for activity time is not sufficient!

PERT Schedule Probability Z = T(S) – T(E) Z = Probability of √SSD(T[E])2 Meeting Schedule Z = T(S) – T(E) T(S) = Scheduled Duration √ΣVar(T[E]) T(E) = Critical Path Duration Z is derived from a table of predetermined probabilities

PERT Activity Times & Variances b t(e) 1-2 17 29 47 30 2-3 6 12 24 13 2-4 16 19 28 20 3-5 4-5 2 5 14 5-6 8

Variance of Activity Estimates b t(e) [(b-a)/6]2 Var 1-2 17 29 47 30 25 2-3 6 12 24 13 9 2-4 16 19 28 20 4 3-5 1 4-5 2 5 14 5-6 8

Critical Path 6 20 13 5 16 30 2 3 4 1 TE = 30 + 13 + 16 + 5 = 64 Var(TE) = 25 + 9 + 1 + 1 = 36

Possible Project Durations TE=64 TS=67 Z = (67 – 64) / √(25 + 9 + 1 + 1) = 0.5 Hence, the probability of meeting the target schedule (Ts) is 0.69 (69%)

Z Table Z Value Probability -2.0 0.02 +2.0 0.98 -1.5 0.07 +1.5 0.93 -1.0 0.16 +1.0 0.84 -0.7 0.24 +0.7 0.76 -0.5 0.31 +0.5 0.69 -0.3 0.38 +0.3 0.62 -0.1 0.36 +0.1 0.54

Z-Table Expanded

Gantt Charts The Gantt chart shows planned and actual progress for a number of tasks displayed against a horizontal time scale It 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 set It can be helpful in expediting, sequencing, and reallocating resources among tasks Gantt charts usually do not show technical dependencies

Gantt Charts There are several advantages to the use of Gantt charts: Even though they may contain a great deal of information, they are easily understood While they may require frequent updating, they are easy to maintain Gantt charts provide a clear picture of the current state of a project They are easy to construct

Drawing Networks Activity-on-Arrow (AOA) networks use arrows to represent activities while nodes stand for events Activity-on-Node (AON) networks use nodes to represent activities with arrows to show precedence relationships The choice between AOA and AON representation is largely a matter of personal preference

Drawing Networks

Hypothetical Network 3 1 2 5 6 4

AOA Network Building Blocks 80 79 Install software Event Activity

Partial Koll Business Center - AOA 4 5 1 3 2 A Application approval D Service availability check C Traffic study B Construction plans

Partial AOA Network 2 3 1 4 A X C B E (A) (B) (C)

Partial AOA Network 2 3 1 4 A B C X E (D) 5 D 2 3 1 4 A B C X E (E) 5 F ?

KOLL BUSINESS CENTER County Engineers Design Department Full AOA Network 2 3 1 4 A 5 B C 10 X 5 15 6 7 8 Y F 10 G 170 H 35 E 15 D 5 Legend KOLL BUSINESS CENTER County Engineers Design Department Activity Duration

Activity-on-Node Network Fundamentals X Y Z Y and Z are preceded by X Y and Z can begin at the same time, if you wish (B) A B C A is preceded by nothing B is preceded by A C is preceded by B (A) J K L M J, K, & L can all begin at the same time, if you wish (they need not occur simultaneously) All (J, K, L) must be completed before M can begin but AA (C) (D) Z is preceded by X and Y AA is preceded by X and Y