A New Concept of Project Robust Schedule – Use of Buffers

Abstract

We propose a new concept of a robust project schedule. The concept is based on the application of time buffers, whose length is known only to the project manager or even only to higher level decision makers, but not to the activity executors, so that the student syndrome does not influence the project realization to a too high extent. The buffers are inserted after each project activity and after each project stage. The role of the buffers is to ensure that delays in the execution of individual activities and stages of single projects do not influence the execution of other projects in the same organization, thus the buffers support a smooth multi project management. The size of buffers should be a function of the features of individual project activities and project stages. This should be judged by experts. We assume that the experts express their opinion as to the satisfying limits of buffer sizes. On the other hand, as buffers prolong the scheduled project completion time, another expert group give the opinion as to the satisfying limits for the scheduled project completion. A model is formulated which determines a compromise schedule, which ensures a satisfying robustness of resource assignments to project activities and stages and at the same time a not too long project makespan. The expert opinions are modeled by means of fuzzy numbers.