Simulation Based Construction Project Schedule Optimization: An Overview on the State-of-the-Art

Simulation Based Construction Project Schedule Optimization: An Overview on the State-of-the-Art

Maximilian Bügler (Technische Universität München, Germany) and André Borrmann (Technische Universität München, Germany)
DOI: 10.4018/978-1-4666-8823-0.ch016
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Abstract

Construction projects require a multitude of procedures and resources for the high diversity of building concepts. Most of such projects are unique in their design and need individual schedule planning to be realized. In order to develop the required schedules, several complex decisions need to be made and several different factors need to be taken into account, including cost, make span, safety, resource sparsity, delivery schedules and geometric constraints. The problem of scheduling the involved processes in an optimal way is called the resource constrained project scheduling problem (RCPSP) and several solution algorithms are available. In addition, simulation based techniques can be used to address more complex constraints and objectives. This chapter presents an overview of traditional optimization procedures for the RCPSP and bridge the gap to simulation based techniques, which are described in detail.
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2. Background

A project scheduling problem can either be defined as a network of activities connected by their respective precedence constraints, or by a network of milestones connected by activities. The first notation with activities as nodes will be used throughout this chapter. Generally each node is associated with a list of resource requirements and a duration value. A node’s incoming arrows define its precedence constraints. To illustrate example problems throughout this chapter the scheme shown in Figure 1 is used. Each of the boxes defines one activity, which are labeled by capital letters. The width of each box is scaled according to the activity’s duration. While in complex problems activities can use multiple types and numbers of resources, the illustrative problems only use a single resource per activity which is indicated by a different hatching for each resource. The arrow from A to B implies that A has to be executed prior to B. In order to illustrate solution schedules the Gantt chart scheme of Figure 2 is used. The horizontal axis defines the time line of the resulting schedule. The boxes are aligned according to their respective execution times. The right hand side extension of boxes, such as for activity E in Figure 2 illustrates the float time of the activity, which will be described in more detail in Section 4.1. Figure 3 illustrates the usage of the resources over time. Again each box corresponds to an activity and the vertical sections correspond to the different resource types.

Figure 1.

Problem notation for resource constrained project scheduling problems. Each rectangle is an activity, arrows indicate precedence constraints, and hatching corresponds to used resources

Key Terms in this Chapter

Discrete-Event Simulation: A method for simulating systems, where the state of the system only changes at discrete points in time, where events happen, such as the completion of an activity.

Makespan: The time difference between start and end time of a schedule.

Schedule: A plan for the execution of a project, assigning start and end times, as well as resources to each activity.

Project: A collection of activities, required resources, and constraints that need to be satisfied for each activities execution.

Activity: A process that requires a certain number of resources and specific predecessor tasks to be finished, in order to be executed. It takes a predefined time to be finished.

Resource: An entity, such as a machine, that is required for the completion of certain activities. After such an activity is completed, the resource becomes available for other activities.

Float Time: The amount of time an activity, or a set of activities, can be shifted, or prolonged within a schedule without changing the remaining schedule and the overall makespan.

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