# WBS: Lowest level OBS: Lowest level

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WBS: Lowest level OBS: Lowest level
Lecture by Junaid Arshad Department of Engineering Management Abridged and adapted by A. M. Al-Araki, sept. 2013 WBS: Lowest level OBS: Lowest level

Topics Covered Network Representation Network Development
Dummy Activity Network Scheduling Practice Problems CPM Network Calculations

Network Representation
Even though a linked Gantt Chart can include precedence relationships between activities, it is an unsuitable tool if these relationships grow beyond a certain complexity. In such situations, the scheduling should be carried out by a network technique. However, the presentation of the schedule to the project participants may still be done in a Gantt Chart format.

Arrows and nodes are used for construction of Network
Arrows and nodes are used for construction of Network. There are two types of network representations: 1. Activity on arrow (AOA) 2. Activity on node (AON) Arrow Node Node

1. Activity on arrow (AOA)
Event In AOA Arrow shows activity and precedence relationships 2. Activity on node (AON) Node Activity In AON Arrow shows precedence relationships only

For structure of network
Network Development Following information is required in order to develop a network: A list of all activities A list of all precedence relationships An estimated duration of each activity (required for network scheduling) For structure of network

Problem 1 Activity Immediate Predecessor (s) A - B C D
Table for network development

Problem 1 Act-ivity Immediate Predecessor A - B C D C D A B
Activity on arrow (AOA) Act-ivity Immediate Predecessor A - B C D C D A B

Problem 1 Activity on arrow (AOA) 2 C A 4 1 B D 3

Problem 1 Activity on node (AON) D C A B START END

Dummy Activity An activity inserted into the network to maintain the logic of the network. A dummy takes zero time and do not consume any resources.

Dummy Activity A precedes B and C, B and C precede D B A 1 2 3 D 4 C 2
Incorrect Display 1 2 3 D 4 C Add a Dummy as shown by dash line below. 2 4 1 A C B D 3 5 Correct Display

Network Scheduling The purpose of network scheduling is
To determine when the project will finish To determine which activities directly influence the project duration Two techniques of network scheduling are: Critical path method (CPM) Program evaluation and review technique (PERT)

PERT and CPM Developed in 1950’s
CPM by DuPont Cooperation for chemical plants (1957) PERT by Booz Allen Hamilton with the U.S. Navy, for Polaris missile (1958) Consider precedence relationships and interdependencies Each uses a different estimate of activity times What circumstances lead the two organizations to develop different, yet similar tools for the management of complex projects? In your discussion of PERT/CPM, you should probably note that PERT helps us identify critical tasks/activities and look at the probability of completing the project by a given date; CPM helps us analyze the cost/time tradeoffs possible if we need to speed the project up.

Questions which may be addressed by
PERT & CPM Is the project on schedule, ahead of schedule, or behind schedule? Is the project over or under cost budget? Are there enough resources available to finish the project on time? If the project must be finished in less than the scheduled amount of time, what is the way to accomplish this at least cost?

Six Common Steps to PERT & CPM
Define the project and prepare the work breakdown structure. Develop relationships among the activities. (Decide which activities must precede and which must follow others.) Draw the network connecting all of the activities Assign time (and/or cost) estimates to each activity Compute the longest time path through the network. This is called the critical path Use the network to help plan, schedule, monitor, and control the project

CPM Network Calculations
CPM calculates a network in several steps: For each event: Earliest possible time: The earliest possible time the event can occur Latest possible time: The latest possible time the event can occur

For each activity: Early start (ES): The earliest possible start time for the activity Early finish (EF): The earliest possible finish time for the activity

For each activity: Late start (LS): The latest possible start time for the activity so as not to delay the completion time of the entire project. Late finish (LF): The latest possible finish time for the activity so as not to delay the completion time of the entire project. Continue to next lecture

Q&A

Topics Covered CPM Calculations for AOA and AON Networks
Slack Time / Float Critical Path, Critical Activity Practice Problems

CPM Calculations for AON Network
Provides activity information Early start (ES) & late start (LS) Early finish (EF) & late finish (LF) Slack (S) / Float (FL) Identifies critical path This and the next several slides illustrate the definitions of terms appropriate to critical path analysis. There are many opportunities for good managers to truly manage a project once they have a PERT network established. For instance, sub-contractors know early start and late start times and the managers know the activities on the critical path upon which to focus effort.

Forward and Backward Pass
Forward pass is a technique to move forward through network diagram. Backward pass is its opposite. Early Start (ES) and Early Finish (EF) use the forward pass technique. Late Start (LS) and Late Finish (LF) use the backward pass technique. Note: If the float of the activity is zero, the two starts (ES and LS) and the two finish (EF and LF) are the same. Hence, If float of activity is zero, ES = LS and EF = LF.

Early Start and Early Finish Steps
Begin at starting event and work forward ES = 0 for starting activities ES is earliest start EF = ES + Activity time EF is earliest finish ES = Maximum EF of all predecessors for non- starting activities

Late Start and Late Finish Steps
Begin at ending event and work backward LF = Maximum EF for ending activities LF is latest finish; EF is earliest finish LS = LF - Activity time LS is latest start LF = Minimum LS of all successors for non-ending activities

AON Network Calculations
ES LS EF LF Earliest Finish Latest Start Earliest Start Activity Name Activity Duration Latest Finish

Slack Time/Float Slack Time is the amount of time an activity may be delayed without affecting the project deadline. This is also referred as float. An activity having zero slack time is called critical activity. The concept of critical activities is that it draws the attention of the project manager to the activities that needs the closest monitoring. Any delay of a critical activity leads to an equivalent delay of the total project. A path having longest duration (completion time) in the network is called critical path.

Gantt Chart for General Hospital Early Start and Finish
ES EF A Build internal components B Modify roof and floor C Construct collection stack D Pour concrete and install frame E Build high-temperature burner F Install pollution control system G Install air pollution device H Inspect and test LS LF This and the following slide illustrate the translation of Early and Late Start and Finish time to Gantt charts.