The following will be discussed in this chapter: Expediting a project, resource loading, resource leveling, allocating scarce resources to projects, allocating scarce resources to several projects, goldratt’s critical chain.
ProjectManagementinPractice SixthEdition Chapter6 AllocatingResourcesto theProject Copyrightâ2016JohnWiley&Sons,Inc 6ư1 Introduction Projectscompetewitheachotherforresources • In either case, one project must wait – • • If resource is used but not consumed, which project must wait to use resource If resource is consumed during use, may not be available for other projects or other projects must wait for replacement One project is delayed Likewise, different activities on the same project may compete for resources Tradeoffs must be made 62 Expediting a Project (Assumptions) Smaller problem to avoid unnecessary arithmetic Problem set in a deterministic world All estimates of task duration are based on normal (or standard) resource loadings 63 Expediting a Project (Approaches) The critical path method Fasttracking a project Project expediting in practice Opportunities before the project begins Opportunities when the project is underway 64 The Critical Path Method • • • • • Normal duration estimates Normal costs Crash duration estimates Crash costs Crash cost per day 65 Notes on Crashing • • Important to make sure the resources required to crash the project are available Technology may be used to crash an activity – • • Using Ditch Witch to dig a ditch rather than adding more workers May have to expedite tasks not on critical path to make resources available to other projects Some tasks cannot be crashed 66 How to Crash • • Start with the normal schedule Select activities to crash, one at a time • Focus on the critical path(s) Select least expensive activity to crash Calculate slope information on activities to crash slope crash cost normal cost crash time normal time 67 An Example of a Normal/Crash Project Table 61 68 A PERT/CPM Example of Crashing a Project, AOA Network Part 1 Figure 61 (Partial) 69 A PERT/CPM Example of Crashing a Project, AOA Network Part 2 Figure 61 (Partial) 610 How Long? • • Each task takes 10 days What is the completion time for each project? – • All three would have the same duration of 50 days Simple project with five tasks takes the same time as complex one with 11 tasks! 648 Part of Problem • • Part of the problem is the assumption that the activity times are known with certainty Assume all activities are normally distributed – – • Mean of 10 Standard deviation of three Each is simulated 200 times 649 Project Completion Time Statistics Based on Simulation Table 65 650 Analysis • • • This example clearly demonstrates how the commonly made assumption of known activity times in practice can lead to quite unrealistic project deadlines The results would have been even more dramatic had the activities required some common resources Similarly, the results would have been more dramatic and realistic had a nonsymmetrical distribution been used to model the activity times 651 Estimating Task Times • • • • Workers often pad time estimates Inflated time estimates tend to create even more problems When workers finish a padded activity early, they often do not let management know they are done yet Worse, workers may perceive they have plenty of time to complete the task and therefore delay starting the task – Goldratt refers to this as the student syndrome 652 Multitasking • • Multitasking is assigning team members to multiple projects and having them allocate their time across these projects There is typically a penalty or cost associated with switching from working on one project to another 653 Sample Project with Multitasking Figure 620 654 Alternative Gantt Charts for Projects A and B Figure 621 655 Common Chain of Events Assuming that activity times are known and that the paths are independent leads to underestimating the actual amount of time needed Because the time is underestimated, project team members tend to inflate their time estimates Inflated time estimates lead to work filling available time, workers not reporting that a task has been completed early An important caveat then becomes that safety time is usually visible to project workers and is often misused Misused safety time results in missed deadlines and milestones 656 Common Chain of Events Continued 10 11 Hidden safety time further complicates the task of prioritizing project activities The lack of clear priorities likely results in poor multitasking Task durations increase as a result of poor multitasking Uneven demand on resources may also occur as a result of poor multitasking In an effort to utilize all resources fully, more projects will be undertaken to make sure that no resources are underutilized Adding more projects further increases poor multitasking 657 Resolving These Problems • • • Goldratt suggests that the key to resolving this is to schedule the start of new projects based on the availability of bottleneck resources He further suggests that time buffers be created between the bottleneck resource and the resources that feed it He also suggests reducing the amount of safety time added to individual tasks and then adding some fraction of the safety time reduced back into the system as safety buffer for the entire project 658 The Critical Chain • • • • Another limitation is the dependency between resources and tasks is often ignored Using traditional approaches, A1C1 is the critical path What if A1 and A2 are not independent Then page A1C1 increases to 22 days Figure 622 659 Addressing Problem Need to consider both precedence relationships and resource dependencies Goldratt proposes thinking in terms of the longest chain of consecutively dependent tasks where such dependencies can arise • • – • Referred to as critical chain There are two potential sources that can delay the project Delay in the tasks that make up the critical chain Delay in activity feeding the critical chain that results in delay of the critical chain 660 Project and Feeder Buffers Figure 623 661 Copyright Copyright © 2016 John Wiley & Sons, Inc All rights reserved. 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The Publisher assumes no responsibility for errors, omissions, or damages, caused by the use of these programs or from the use of the information herein 662 ... normal (or standard) resource loadings 63 Expediting a Project (Approaches) The critical path method Fasttracking a project Project expediting in practice Opportunities before the project begins Opportunities when the project is underway... that this project is timecritical and needs to be finished as early as possible Project manager may during project that it needs to be finished earlier Something delays the project and time needs to be made up... An expediting technique in which one phase of the project is started before preceding phases are completed Used in the construction industry when the building phase is started before the design