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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
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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.
Arrow Node Node 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)
Activity Event Event In AOA Arrow shows activity and precedence relationships 2. Activity on node (AON) Node Activity In AON Arrow shows precedence relationships only 1. Activity on arrow (AOA) NB! Okto_arrowed-line & node
Network Development For structure of network 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)
Problem 1 C D Activity on arrow (AOA) A B
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 2 1 4 2 3 4 5 1 3 B A C D A precedes B and C, B and C precede D B A Incorrect Display D C Add a Dummy as shown by dash line below. 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
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
Continue to next lecture 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.
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
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
ES EF 1 2 3 4 5 6 7 8 9 10 1112 13 1415 16 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 Gantt Chart for General Hospital Early Start and Finish LF LS
Slack Time/Float SlackTimeis 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.