XI- ADVANTAGES SCHEDULING PROCESS

• Use of Advanced Scheduling Techniques • Scheduling with Uncertain Durations • Calculations for Monte Carlo Schedule Simulation • Crashing and Time/Cost Tradeoffs • Scheduling in Poorly Structured Problems • Improving the Scheduling Process

11.1 Use of Advantaged Scheduling Techniques

• scheduling in the face of uncertain estimates on activity durations,

• integrated planning of scheduling and resource allocation,

• scheduling in unstructured or poorly formulated circumstances.

11.2 Scheduling with UncertainDurations

• During the preliminary planning stages for a project, the uncertainty in activity durations is particularly large since the scope and obstacles to the project are still undefined. Activities that are outside of the control of the owner are likely to be more uncertain.

• Two simple approaches to dealing with the uncertainty in activity durations warrant some discussion before introducing more formal scheduling procedures to deal with uncertainty. First, the uncertainty in activity durations may simply be ignored and scheduling done using the expected or most likely time duration for each activity

11.2 Scheduling with UncertainDurations

• A second simple approach to incorporation uncertainty also deserves mention. Many managers recognize that the use of expected durations may result in overly optimistic schedules, so they include a contingency allowance in their estimate of activity durations.

11.3 Calculations for Monte Carlo SchedulemSimulation

• The various steps involved in forming a network plan and estimating the characteristics of the probability distributions for the various activities have been completed. Given a plan and the activity duration distributions, the heart of the Monte Carlo simulation procedure is the derivation of a realization or synthetic outcome of the relevant activity durations. Once these realizations are generated, standard scheduling techniques can be applied.

11.4 Crashing and Time/Cost Tradeoffs

• Activity durations can often vary depending upon the type and amount of resources that are applied. Assigning more workers to a particular activity will normally result in a shorter duration. Greater speed may result in higher costs and lower quality, however.

11.4 Crashing and Time/Cost Tradeoffs

• A simple representation of the possible relationship between the duration of an activity and its direct costs appears in Figure Considering only this activity in isolation and without reference to the project completion deadline, a manager would undoubtedly choose a duration which implies minimum direct cost, represented by Dij and Cij in the figure

11.5 Scheduling in Poorly Structured Problems

• The previous discussion of activity scheduling suggested that the general structure of the construction plan was known in advance. With previously defined activities, relationships among activities, and required resources, the scheduling problem could be represented as a mathematical optimization problem. Even in the case in which durations are uncertain, we assumed that the underlying probability distribution of durations is known and applied analytical techniques to investigate schedules.

• Two important problems must be borne in mind in applying a "generate-and-test" strategy. First, the number of possible plans and schedules is enormous, so considerable insight to the problem must be used in generating reasonable alternatives. Secondly, evaluating alternatives also may involve considerable effort and judgment. As a result, the number of actual cycles of alternative testing that can be accomadated is limited.

11.6 Improving the Scheduling Process

• The importance of scheduling in insuring the effective coordination of work and the attainment of project deadlines is indisputable. For large projects with many parties involved, the use of formal schedules is indispensable.

• The network model for representing project activities has been provided as an important conceptual and computational framework for planning and scheduling. Networks not only communicate the basic precedence relationships between activities, they also form the basis for most scheduling computations.