Traditional PERT Research Articles

Application of Monte Carlo simulation and PERT/CPM techniques in planning of construction projects: A Case study

Construction project scheduling and monitoring is challenging in today's very dynamic business environment. In this study, a project execution tracking system in a medium‒sized construction company was studied. Two different methods were proposed as problem solution for project scheduling and monitoring. Traditional CPM and PERT methods, and Monte Carlo simulation as risk analysis tool were used in this case study. The results show that 186 working days (which is optimistic estimate) is required to finish a luxury villa is determined by CPM method, while Monte Carlo simulation implies that there is 50% of chance that the luxury villa will be done in 205 days, but still there is a risk of 50% that the villa construction may be delayed.

Incorporation of activity sensitivity measures into buffer management to manage project schedule risk

Critical Chain Scheduling and Buffer Management (CC/BM) has shown to provide an effective approach for building robust project schedules and to offer a valuable control tool for coping with schedule variability. Yet, the current buffer monitoring mechanism faces a problem of neglecting the dynamic feature of the project execution and related activity information when taking corrective actions. The schedule risk analysis (SRA) method in a traditional PERT framework, on the other hand, provides important information about the relative activity criticality in relation to the project duration which can highlight management focus. It is implied, however, that control actions are independent from the current project schedule performance. This paper attempts to research these defects of both tracking methods and proposes a new project schedule monitoring framework by introducing the activity cruciality index as a trigger for effective expediting to be integrated into the buffer monitoring process. Furthermore, dynamic action threshold settings that depend on the project progress as well as the buffer penetration are presented and examined in order to exhibit a more accurate control system. Our computational experiment demonstrates the relative dominance of the integrated schedule monitoring methods compared to the predominant buffer management approach in generating better control actions with less effort and an increased tracking efficiency, especially when the increasing buffer trigger point is combined with decreasing sensitivity action threshold values.

East Aurora Fire Department

Case study enabling a contrast between traditional PERT analysis and broader spreadsheet simulation. Teaching notes and spreadsheet models available from author.

Progress Risk Assessment for Spliced Network of Engineering Project Based on Improved PERT

Aimed at the deficiency of the traditional PERT method in the risk assessment for engineering project progress, this paper has improved PERT method, so as to make it more suitable for engineering project risk assessment of spliced network. Firstly, in calculating project activity duration, it adopts response management theory and introduces double-buffering zone, so that the calculated project activity duration is more approximate to the realistic one. Meanwhile, the paper takes advantage of equivalent-weight probability method to revise the main path, so that the calculated project duration is more suitable for the realistic situation. Finally, the paper has further demonstrated the feasibility of the method by an engineering project case study.

The effect of systemic errors on optimal project buffers

Existing mathematical models for setting buffers for time or cost in project management assume that project activities are statistically independent. This leads to a highly counterintuitive and damaging conclusion that project buffers should become relatively negligible for projects with long chains of activities. We present a model that considers the statistical dependence between activities caused by estimation bias. We show that if relatively high service levels are desired, this imposes a positive lower bound on the buffer as a data-based fraction of the estimated project duration or budget. We also introduce a new approach for collecting data and estimating the parameters necessary to implement the model. This approach places a smaller burden on decision makers than traditional PERT: they provide single point estimates for means, while variance elements and bias correction are computed electronically using historical data.

An approximation of the activity duration distribution in PERT

PERT is widely used as a tool for managing large-scale projects. The traditional PERT approach uses the beta distribution as the distribution of activity duration and estimates the mean and the variance of activity duration based on the “pessimistic”, “optimistic” and “most likely” time estimates. Several authors have modified the original three point PERT estimators to improve the accuracy of the estimates. This article proposes new approximations for the mean and the variance of activity based on “pessimistic”, “optimistic” and “most likely” time estimates. By numerical comparison with actual values, the proposal is shown as more accurate than the original PERT estimates and its modifications. Another advantage of the proposed approximation is that it requires no assumptions about the parameters of the beta distribution as in the case of existing ones. Scope and purpose The traditional PERT model uses beta distribution as the distribution of activity duration and estimates the mean and the variance of activity duration using “pessimistic”, “optimistic” and “most likely” time estimates proposed by an expert. In the past several authors have modified the original PERT estimators to improve the accuracy. This article proposes new approximations for the mean and the variance of activity duration which are more accurate than the original PERT estimates and their modifications. Another advantage of the proposal is that it is not based on any assumptions about the parameters of the beta distribution as in the case of the existing ones.

Analysis of Activity Networks under Uncertainty

A practical probabilistic technique is presented for evaluating the distribution of project completion time. Upper and lower bounds on the completion-time probability are established and form the basis for the probabilistic network evaluation technique (PNET) algorithm. The mean durations and the correlations among the network paths are the main parameters used to generate a set of representative paths from which the probability distribution of completion time is evaluated. This technique overcomes the shortcomings implicit in PERT, although its application is almost as simple as the traditional PERT method. Several construction projects are presented as examples to illustrate the algorithm. The results obtained by PNET are shown to be in very good agreement with simulation runs, thus verifying its validity; computation times, however, are several order-of-magnitude less than those required by simulation.