PLANNING & SCHEDULING

Transcription

1 PLANNING & SCHEDULING 1 Planning & Scheduling Planning: Process of choosing the method and order of work Scheduling: Process of determining the interrelationship of associated timings of operations. 2 Liaqat Ali Qureshi 1

2 Planning & Scheduling Network Schedules Non - Network Schedules (Bar Charts) CPM PERT Monte Carlo Simulation Techniques 3 Network Scheduling Network Scheduling is a method of scheduling activities by joining them in a series of interconnected links which reflect relationships of activities as assigned by the planner. 4 Liaqat Ali Qureshi 2

3 Basic Assumptions for a Network Schedule 1- The project can be broken down into a group of activities. 2- Each activity can be assigned a duration. 3- The logic relationship between activities are known and fixed in the network chain. 5 Techniques for Network Scheduling 1- CPM (Critical Path Method) It is the most popular network-scheduling technique used in construction. Developed in the mid fifties by Morgan Walker & James E. Kelly for managing the construction, overhaul, and shutdown of large chemical plants. Uses only one possible project duration and the process is called deterministic. 6 Liaqat Ali Qureshi 3

4 Techniques for Network Scheduling (- ctd -) 2- PERT (Program Evaluation & Review Techniques) Developed in the mid fifties but not in connection with CPM by the U.S. Navy for the research & development of their Polaris Missile Program. Uses probability distributions rather than fixed values and, hence, termed as stochastic. 7 Techniques for Network Scheduling (- ctd -) 3- MONTE CARLO SIMULATION TECHNIQUES Not new technique but its practical use in network scheduling is new, due to the availability of fast, affordable computers. It utilizes simulation to predict a project duration by using random numbers to assign probable durations to activities and then solving the CPM algorithm for project duration. By repeating the process many times, one can produce a distribution for the probable project duration. 8 Liaqat Ali Qureshi 4

5 CRITICAL PATH METHOD (CPM) (BASIC STEPS) Splitting of the project into work activities Determining logic relationships/interrelationships between activities. Construction of Network Diagrams. Assigning durations to work activities. (PERT and CPM use different techniques for this) CPM Calculations resulting in start times, finish times and float calculations of activities. Marking of Critical Path Construction of Bar Charts / Time phased diagrams. 9 ACTIVITY An element of work performed during the course of a project. Or An amount of work that can be identified so that we know what it involves and can recognize, when it starts and finishes. A real activity normally has an expected duration, an expected cost, and expected resource requirements. A list of activities preceeding any given activity is called PA list. A list of activities immediately preceeding any given activity is called IPA list. 10 Liaqat Ali Qureshi 5

6 CLASSIFICATION OF ACTIVITIES 1- PROCUREMENT It involves all things that must be brought to the job that require time, such as permanent materials, temporary materials, workers, money, equipment and utilities. 2- CONSTRUCTION It includes the activities necessary to assemble and erect the facility. 3- MANAGEMENT It includes all items necessary for the project but not specially identifies in the first or second category. 11 ACTIVITY DURATIONS Activity duration is forecasted by any one or more of the several means, including: (1) Check Past Records. (2) Check Standards and / or cost guides, if available. (3) Ask the workers, who will do it (4) make an educated guess Any time units may be allotted to activity durations like days, hours, weeks, months, shifts, etc. In CPM, a single duration is forecasted for an activity. In PERT (Program Evaluation & Review Techniques), 3 durations are forecasted for an activity and mean taken by weighted average method. Then, Project s Duration or any Event Completion Time is calculated by probability distribution. 12 Liaqat Ali Qureshi 6

7 Network Diagrams Any schematic display of the logical relationship of project activities. Always drawn from left to right to reflect project chronology. Usually a combination of arrows and nodes. A Network for a project is not unique. Mainly of two types: 1. Arrow diagram / Activity-on-arrow diagram 2. Node diagram / Precedence diagram /Activity-on-node diagram 13 ARROW DIAGRAMS Activity is shown by arrow. Relationship between activities shown by nodes / events. Activity i Duration j A B C D Length of arrow has no relation with the duration/size of activity. It is just a symbol. Customarily arrow always starts from left to right. Liaqat Ali Qureshi 7

8 EVENT NUMBERING Events are numbered in an Arrow Diagram. For any given Activity, the head event number should be greater than the tail event number i.e. i < j Each Activity should have a unique i & j pair. Situation in Figure 2.14 is not allowed. 15 MILESTONES Events of some special significance are called Milestones. It is just name given to an event, otherwise the milestone is treated like other events in the CPM calculations. 16 Liaqat Ali Qureshi 8

9 DUMMY ACTIVITIES An activity having zero duration and zero cost (and uses zero resources) is called Dummy Activity. Dummy Activity is represented by Dashed Lined Arrow. A Dummy Activity may be ---- Logic Dummy To fulfill logic relationship ---- Numbering Dummy To avoid same i, j pair for two activities ---- Start / Finish Dummy To give single start or finish activity in the network. 17 Logic Dummy Suppose in a project, B depends on A and D depends on C, as shown in Fig (a) in the next slide. Suppose B depends on A & C and D depends on C only. If Fig (c) is used to show it, it creates an extra condition that D depends on both C and A. Use of a dummy simplifies the situation as shown in fig (b). Such a dummy is called Logic Dummy. 18 Liaqat Ali Qureshi 9

10 Numbering Dummy 19 Start/Finish Dummy Liaqat Ali Qureshi 10

11 ARTIFICIAL ACTIVITY When a time delay is needed in a construction sequence, an Artificial Activity is introduced. An Artificial Activity is associated with time duration but has zero cost. 21 ACTIVITY CROSSOVER Activity crossover is not allowed in Arrow diagrams. However, if unavoidable, one of the following configurations may be adopted: 22 Liaqat Ali Qureshi 11

12 HOW TO DRAW AN ARROW DIAGRAM? We draw an arrow diagram with patience and a fair amount of paper, lead pencil, and erasers. On the first draft of the arrow diagram, we simply try to get the logic correct. Since we probably will have some arrows going backward, be sure to put the directional head on them, at this point. Don t worry about numbering the nodes yet. From a given IPA list, arrow diagram will not be unique. An efficient arrow diagram will be that having minimum number of dummies. There are two techniques for constructing arrow diagram from IPA list. 23 Technique 1 Mark starting and ending activities on the IPA list. Starting activities have no IPA while ending activities are not IPA s of any other activity. Draw the last activity on the right side of the page and then draw activities which are in its IPA list. In this way work backward, right to left, drawing the IPA s and connecting them to the proper activities. At the last, dress up the network as per arrow diagram s requirements. This method gives a fairly neat drawing on the first draft but requires a lot of erasing and redrawing. 24 Liaqat Ali Qureshi 12

13 EXAMPLE 1 Liaqat Ali Qureshi 13

14 27 Example 2 ACTIVITY IPA ACTIVITY IPA A F A, B, C B G E, F C H D, G D A I D, G E A, B, C Liaqat Ali Qureshi 14

15 ACTIVITY IPA ACTIVITY IPA A F A, B, C B G E, F C H D, G D A I D, G E A, B, C Liaqat Ali Qureshi 15

16 Technique 2 It produces a diagram much faster but not as neatly. We draw each activity as a single activity i.e., one arrow and two nodes. Those activities that obviously occur early in the project should be drawn on the left of the sheet, and those that occur late in the project should be drawn to the right. The other activities, which are somewhere in the middle of the project, should just be spread around. After all activities are drawn, connect the i node of each activity to the j node of each of its IPA by using a dummy. Now we have an arrow diagram that is perfectly logical but hard to use. 31 Technique 2 (-ctd-) The next step is to clean up the diagram by getting rid of unnecessary dummies. This is done by taking one dummy at a time and asking the question If I shrink this dummy, combining the nodes at either end, will it change the network logic? If the answer is yes, then leave it in; if the answer is no, just shrink and combine the j node of the preceding activity with i node of the succeeding activity. After this reduction process, redraw the diagram, trying to follow the rules given. 32 Liaqat Ali Qureshi 16

17 EXAMPLE 1 ACTIVITY IPA A B C D E F A A B, C C C Liaqat Ali Qureshi 17

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19 37 Example 2 ACTIVITY IPA ACTIVITY IPA A F A, B, C B G E, F C H D, G D A I D, G E A, B, C 38 Liaqat Ali Qureshi 19

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24 47 Figure shows a different way of drawing the arrow diagram, but with the same logic: 48 Liaqat Ali Qureshi 24

25 Node Diagrams Activities shown by Nodes, relationship between activities shown by arrows or links. Nodes may be circles, squares, or rectangles. These are easier to construct. Generally no need of dummies. Instead dummies used only to give single start or finish. Crossing of arrows or links is allowed. CPM calculations are similar to arrow diagrams. 49 In Figure below, C is the activity name and 10 is the activity duration shown in a square node. 50 Liaqat Ali Qureshi 25

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27 HOW TO CONSTRUCT NODE DIAGRAMS? Construction of Node diagrams is very easy as compared to arrow diagrams. Sequence steps (SS) are assigned to each activity. Any activity is given a sequence step higher than its IPA s. If activity B follows activity A and A was on SS1, B will be on SS2. We start the diagram by placing the sequence steps across the page and arranging the activities vertically above the proper step. Activities are then connected with straight lines, according to their IPA s. 53 EXAMPLE 1 ACTIVITY IPA SS A B A 2 C A 2 D B, C 3 E C 3 Fn D, E 4 54 Liaqat Ali Qureshi 27

28 55 Example 2 ACTIVITY IPA ACTIVITY IPA A F A, B, C B G E, F C H D, G D A I D, G E A, B, C 56 Liaqat Ali Qureshi 28

29 As there are more than one starting and ending activities, add a start dummy (St) and a finish dummy (Fn) ACTIVITY IPA SS ACTIVITY IPA SS St F A, B, C 3 A St 2 G E, F 4 B St 2 H D, G 5 C St 2 I D, G 5 D A 3 Fn H, I 6 E A, B, C Liaqat Ali Qureshi 29

30 THANKS 59 Liaqat Ali Qureshi 30