3 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.
4 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)ArrowNodeNode
5 1. Activity on arrow (AOA) EventIn AOA Arrow shows activity and precedence relationships2. Activity on node (AON)NodeActivityIn AON Arrow shows precedence relationships only
6 For structure of network Network DevelopmentFollowing information is required in order to develop a network:A list of all activitiesA list of all precedence relationshipsAn estimated duration of each activity (required for network scheduling)For structure of network
7 Problem 1 Activity Immediate Predecessor (s) A - B C D Table for network development
8 Problem 1 Act-ivity Immediate Predecessor A - B C D C D A B Activity on arrow (AOA)Act-ivityImmediatePredecessorA-BCDCDAB
11 Dummy ActivityAn activity inserted into the network to maintain the logic of the network. A dummy takes zero time and do not consume any resources.
12 Dummy Activity A precedes B and C, B and C precede D B A 1 2 3 D 4 C 2 Incorrect Display123D4CAdd a Dummy as shown by dash line below.241ACBD35Correct Display
13 Network Scheduling The purpose of network scheduling is To determine when the project will finishTo determine which activities directly influence the project durationTwo techniques of network scheduling are:Critical path method (CPM)Program evaluation and review technique (PERT)
14 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 interdependenciesEach uses a different estimate of activity timesWhat 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.
15 Questions which may be addressed by PERT & CPMIs 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?
16 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 activitiesAssign time (and/or cost) estimates to each activityCompute the longest time path through the network. This is called the critical pathUse the network to help plan, schedule, monitor, and control the project
17 CPM Network Calculations CPM calculates a network in several steps:For each event:Earliest possible time: The earliest possible time the event can occurLatest possible time: The latest possible time the event can occur
18 For each activity:Early start (ES): The earliest possible start time for the activityEarly finish (EF): The earliest possible finish time for the activity
19 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
21 Topics Covered CPM Calculations for AOA and AON Networks Slack Time / FloatCritical Path, Critical ActivityPractice Problems
22 CPM Calculations for AON Network Provides activity informationEarly start (ES) & late start (LS)Early finish (EF) & late finish (LF)Slack (S) / Float (FL)Identifies critical pathThis 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.
23 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.
24 Early Start and Early Finish Steps Begin at starting event and work forwardES = 0 for starting activitiesES is earliest startEF = ES + Activity timeEF is earliest finishES = Maximum EF of all predecessors for non- starting activities
25 Late Start and Late Finish Steps Begin at ending event and work backwardLF = Maximum EF for ending activitiesLF is latest finish; EF is earliest finishLS = LF - Activity timeLS is latest startLF = Minimum LS of all successors for non-ending activities
27 Slack Time/FloatSlack 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.
28 Gantt Chart for General Hospital Early Start and Finish ES EFA Build internal componentsB Modify roof and floorC Construct collection stackD Pour concrete and install frameE Build high-temperature burnerF Install pollution control systemG Install air pollution deviceH Inspect and testLSLFThis and the following slide illustrate the translation of Early and Late Start and Finish time to Gantt charts.