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Lecture#09. PLANNING ENGINEERING AND PROJECT MANAGEMENT. By Lec. Junaid Arshad. DEPARTMENT OF ENGINEERING MANAGEMENT. Topics Covered. Program Evaluation and Review Technique (Pert) Project Crashing Sample Problems. Program Evaluation and Review Technique. 2.
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Lecture#09 PLANNING ENGINEERING AND PROJECT MANAGEMENT By Lec. Junaid Arshad DEPARTMENT OF ENGINEERING MANAGEMENT
Topics Covered • Program Evaluation and Review Technique (Pert) • Project Crashing • Sample Problems
Program Evaluation and Review Technique 2 Pert calculates the expected durations for all activities and then does an ordinary CPM calculation of the network using these expected values as durations.The expected value and variance can be calculated as: TE=(a+ b +4m)/6 (already discussed) Var=V= 1/36 (b - a) The variance is a measure of uncertainty of the duration. The larger variance, the larger is the uncertainty.
Program Evaluation and Review Technique 1/2 Standard deviation = = ( V ) Probability Pr = Φ (D – T)/ D= deadline / desired completion time T= project completion time Φ= normal distribution (from table)
Problem 09 (Use Pert Technique on P-04)
Problem 09 (Pert Solution) The network is calculated using the expected values (TE). The critical path is A-D-H. Project completion time T= Ta+Td+Th = 11+20+13 = 44 Variance V= Va + Vd + Vh = 1.78+7.11+1.78= 10.67
Problem 09 (Pert Solution) The variance as such does not provide much practically useful information about uncertainty. It is used to calculate probability, which can then be used as a decision parameter. For example, project manager would like to know what is the probability of reaching the 40-days deadline calculated by CPM method.
Problem 09 (Pert Solution) 1/2 1/2 The chance of meeting the deadline is 11 percent only. Pr = Φ (40 – 44) / 3.266 = Φ (-1.23) = 0.11 Standard deviation= = (V) = (10.67) = 3.266 Probability Pr = Φ (D – T) / D= deadline / desired completion time=40 T= project completion time=44
Problem 09 (Pert Solution) 0.90 = Φ (D – 44) / 3.266 Φ(1.28)= Φ (D – 44) / 3.266 D= 48.2 In order to have 90 percent guarantee against a delay, the deadline should be 49 days. R E S U L T What deadline project manager should give if he/she wants 90 percent probability of finishing on or before the deadline? If this deadline is D, using the formula
Comments on Pert Program evaluation and review technique (PERT) allows activity duration with uncertainty. It assumes that there is no underlying connection leading to simultaneous duration variation of two or more activities. If activity X is delayed, this does not lead to a similar delay of activity Y. This is, of course, a questionable assumption. Quite often there are activities that are connected. For example, a delay of an activity may be caused by a shortage of labor. In this case it is reasonable to believe that this is the case for other activities performed in the same region.
Project Crashing • Crashing means reducing project time (total project completion time) • The objective of crashing is to reduce the entire project completion time by a certain amount at the least cost. • Crashing is achieved by reducing the activity (s) times in a network. • Activity time can be reduced by utilizing additional resources i-e additional labor, more equipment and so on.
Project Crashing • Although shortening or crashing activity times can be expensive; doing so might be worthwhile. This is also referred as cost-time trade-offs.
Project Crashing Crash Cost and Crash Duration Crash cost is defined as the cost associated with the fastest way of doing something and results in what we call the crash duration. Normal Cost and Normal Duration: Normal cost is defined as the cost associated with the most economical way of doing something and results in what we call the normal duration.
Project Crashing • Rules: • Crash the activities on the critical path. As a result of crashing, a parallel non-critical path may become new critical path. • Start crashing with least cost of crashing per unit time, crash the most costly activity if required, last of all.
Project Crashing 2 3 4 6 1 4 2 3 3 Reduce it to 06 days Total Project Time 07 days
Project Crashing crash cost per unit time
Project Crashing Activity 1-2 and Activity 2-4; both are on critical path. The project completion time can be reduced to six days by crashing either 1-2 or 2-4 by one day. It costs $20 per day to crash activity 1-2 and $25 per day to crash activity 2-4. Therefore it is less costly to crash activity 1-2 by one day in order to achieve an over all project completion time of six days.
Problem 10 Problem 10 The data of activities, activity precedence, activity normal and crash times and costs for a pipe line renewal is given in the table on next slides. a) Develop a network for the project. b) Determine the project completion time with normal time of activities. c) Crash the project to reduce the project completion time with least incremental cost. Note: Time is given in days and cost in rupees.
