A classification of predictive-reactive project scheduling procedures.

The vast majority of the project scheduling research efforts over the past several years have concentrated on the development of workable predictive baseline schedules, assuming complete information and a static and deterministic environment. During execution, however, a project may be subject to numerous schedule disruptions. Proactive-reactive project scheduling procedures try to cope with these disruptions through the combination of a proactive scheduling procedure for generating predictive baseline schedules that are hopefully robust in that they incorporate safety time to absorb anticipated disruptions with a reactive procedure that is invoked when a schedule breakage occurs during project execution.proactive-reactive project scheduling; time uncertainty; stability; timely project completion; preselective strategies; resource constraints; trade-off; complexity; stability; management; makespan; networks; subject; job;

The trade-off between stability and makespan in resource-constrained project scheduling.

During the last decade a lot of research efforts in the project scheduling literature have concentrated on resource-constrained project scheduling under uncertainty. Most of this research focuses on protecting the project due date against disruptions during execution. Few efforts have been made to protect the starting times of intermediate activities. In this paper, we develop a heuristic algorithm for minimizing a stability cost function (weighted sum of deviations between planned and realized activity starting times). The algorithm basically proposes a clever way to add intermediate buffers to a minimal duration resource-constrained project schedule. We provide an extensive simulation experiment to investigate the trade-off between quality robustness (measured in terms of project duration) and solution robustness(stability). We address the issue whether to concentrate safety time in so-called project and feeding buffers in order to protect the planned project completion time or to scatter safety time throughout the baseline schedule in order to enhance stability.Stability; Project scheduling; Scheduling; Research; Uncertainty; Time; Heuristic; Simulation; Quality; Quality robustness; Robustness; Order; Scatter;

The use of buffers in project management: the trade-off between stability and makespan.

During execution, projects may be subject to considerable uncertainty, which may lead to numerous schedule disruptions. Recent research efforts have focused on the generation of robust project baseline schedules that are protected against possible disruptions that may occur during schedule execution. The fundamental research issue we address in this paper is the potential trade-off between the quality robustness (measured in terms of project duration) and solution robustness (stability, measured in terms of the deviation between the planned and realised start times of the projected schedule). We provide an extensive analysis of the results of a simulation experiment set up to investigate whether it is beneficial to concentrate safety time in project and feeding buffers, or whether it is preferable to insert time buffers that are scattered in a clever way throughout the baseline project schedule in order to maximize schedule stability.Management; Project management; Project scheduling; Quality; Quality robustness; Robustness; Schedule stability; Scheduling; Simulation; Stability; Time; Uncertainty;

A methodology for integrated risk management and proactive scheduling of construction projects.

An integrated methodology is developed for planning construction projects under uncertainty. The methodology relies on a computer supported risk management system that allows to identify, analyze and quantify the major risk factors and derive the probability of their occurrence and their impact on the duration of the project activities. Using project management estimates of the marginal cost of activity starting time disruptions, a proactive baseline schedule is developed that is suffciently protected against the anticipated disruptions with acceptable project makespan performance. The methodology is illustrated on a real life application.Risk; Risk management; Management; Scheduling; Construction; Planning; Uncertainty; Factors; Probability; Impact; Project management; Cost; Time; Performance; Real life;

A heuristic methodology for solving spatial aresource-constrained project scheduling problems.

In this paper we present a heuristic methodology for solving resource-constrained project scheduling problems with renewable and spatial resources. We especially concentrate on spatial resources that are encountered in construction projects, but our analysis can easily be generalized to other sectors. Our methodology is based on the application of a schedule generation scheme on apriority list of activities. We explain why the parallel schedule generation scheme is not applicable for projects with spatial resources. We introduce a procedure for transforming priority lists into precedence and resource feasible lists that avoid deadlocks on the spatial resources. We conclude from a computational experiment on two sets of instances that priority rules performing well for the regular resource-constrained project scheduling problem also perform well in the presence of spatial resources and allow to effectively solve large problems in very short CPU time.Construction; Resource-constrained project scheduling; Spatial resources; Heuristic; Project scheduling; Scheduling; Problems; Sector; Rules; Time;

The trade-off between stability and makespan in resource-constrained project scheduling.

During the last decade, considerable research efforts in the project scheduling literature have concentrated on resource-constrained project scheduling under uncertainty. Most of this research focuses on protecting the project due date against disruptions during execution. Few efforts have been made to protect the starting times of intermediate activities. In this paper, we develop a heuristic algorithm for minimizing a stability cost function (weighted sum of deviations between planned and realized activity starting times). The algorithm basically proposes a clever way to scatter time buffers throughout the baseline schedule. We provide an extensive simulation experiment to investigate the trade-off between quality robustness (measured in terms of project duration) and solution robustness (stability). We address the issue whether to concentrate safety time in so-called project and feeding buffers in order to protect the planned project completion time or to scatter safety time throughout the baseline schedule in order to enhance stability.Project management; Scheduling/sequencing; Simulation methods;

Proactive-reactive procedures for robust project scheduling.

The vast majority of research efforts in project scheduling concentrates on developing procedures to generate workable baseline schedules that minimize the project makespan in a deterministic environment. However, a real-life project is inevitably subject to uncertainty during execution. This dissertation aims at introducing procedures that cope with disruptions during execution. We limit ourselves to the treatment of time uncertainties caused by the fact that actually realized activity durations during project execution may deviate from the expected activity durations. When dealing with uncertainty in a scheduling environment, there are, generally spoken, two main approaches. Proactive scheduling focuses at incorporating safety in the schedule to absorb future disruptions, while reactive scheduling denotes how to react when a disruption occurs. Both approaches are inescapably related. We will investigate in how several proactive-reactive scheduling decisions can help a project manager to increase the quality of a project. The text of this dissertation is organized as follows. Chapter 1 introduces the problem of proactive-reactive project scheduling and situates it in the extensive project scheduling literature. Chapter 2 formulates the problem at hand and defines the concepts required in the remainder of the thesis. The trade-off between makespan and stability in project scheduling of Chapter 3 justifies the research efforts made in Chapters 4, 5 and 6 to add safety to the baseline schedule. Mainly two approaches to add safety are discussed in this thesis. First, a schedule is made proactive in Chapter 4 by deciding how the resources flow throughout the project. Next in Chapter 5, we develop efficient and effective procedures to add idle time (buffers) into a schedule to anticipate unforeseen events. Chapter 6 contains an extension of Chapters 4 and 5 by merging scheduling, resource allocation and buffer allocation decisions into an integrated approach. The reactive procedures that are required to decide how to react on disruptions that cannot be absorbed by the baseline schedule are introduced in Chapter 7. In Chapter 8 an extensive simulation-based experiment is set-up to evaluate several predictive-reactive resource-constrained project scheduling procedures proposed in the previous chapters. Chapter 9 applies the proactive-reactive project scheduling methodology on a real-life project that stems from our experience in the Belgian construction industry. Accordingly, a risk management framework is introduced to detect and analyze the risks that constitute the uncertainty implied in the project. In a last chapter, some overall conclusions and recommendations are provided.

Proactive-reactive procedures for robust project scheduling

The vast majority of research efforts in project scheduling concentrates on developing procedures to generate workable baseline schedules that minimize the project makespan in a deterministic environment. However, a real-life project is inevitably subject to uncertainty during execution. This dissertation aims at introducing procedures that cope with disruptions during execution. We limit ourselves to the treatment of time uncertainties caused by the fact that actually realized activity durations during project execution may deviate from the expected activity durations. When dealing with uncertainty in a scheduling environment, there are, generally spoken, two main approaches. Proactive scheduling focuses at incorporating safety in the schedule to absorb future disruptions, while reactive scheduling denotes how to react when a disruption occurs. Both approaches are inescapably related. We will investigate in how several proactive-reactive scheduling decisions can help a project manager to increase the quality of a project. The text of this dissertation is organized as follows. Chapter 1 introduces the problem of proactive-reactive project scheduling and situates it in the extensive project scheduling literature. Chapter 2 formulates the problem at hand and defines the concepts required in the remainder of the thesis. The trade-off between makespan and stability in project scheduling of Chapter 3 justifies the research efforts made in Chapters 4, 5 and 6 to add safety to the baseline schedule. Mainly two approaches to add safety are discussed in this thesis. First, a schedule is made proactive in Chapter 4 by deciding how the resources flow throughout the project. Next in Chapter 5, we develop efficient and effective procedures to add idle time (buffers) into a schedule to anticipate unforeseen events. Chapter 6 contains an extension of Chapters 4 and 5 by merging scheduling, resource allocation and buffer allocation decisions into an integrated approach. The reactive procedures that are required to decide how to react on disruptions that cannot be absorbed by the baseline schedule are introduced in Chapter 7. In Chapter 8 an extensive simulation-based experiment is set-up to evaluate several predictive-reactive resource-constrained project scheduling procedures proposed in the previous chapters. Chapter 9 applies the proactive-reactive project scheduling methodology on a real-life project that stems from our experience in the Belgian construction industry. Accordingly, a risk management framework is introduced to detect and analyze the risks that constitute the uncertainty implied in the project. In a last chapter, some overall conclusions and recommendations are provided.status: publishe

An investigation of efficient and effective predictive-reactive project scheduling procedures

The vast majority of the project scheduling research efforts over the past several years have concentrated on the development of workable predictive baseline schedules, assuming complete information and a static and deterministic environment. During execution, however, a project may be subject to numerous schedule disruptions. Proactive-reactive project scheduling procedures try to cope with these disruptions through the combination of a proactive scheduling procedure for generating predictive baseline schedules that are hopefully robust in that they incorporate safety time to absorb anticipated disruptions with a reactive procedure that is invoked when a schedule breakage occurs during project execution. In this paper we discuss the results obtained by a large experimental design set up to evaluate several predictive-reactive resource-constrained project scheduling procedures under the composite objective of maximizing both the schedule stability and the timely project completion probabilitystatus: publishe