Assessing project schedule risk with contingent tasks by spreadsheet-based simulation

Abstract

Construction projects have become increasingly complex and dynamic for contractors, because of trends toward a larger scope of contract. An example is a design and build (D/B) contract with a higher level of uncertainty that makes planning more difficult. There is a need for a practical way of assessing schedule risk in order to accommodate the increased importance of contingent tasks and alternative routes in completing a project. This article presents an approach that is based on an extended precedence network to integrate contingent tasks, both those occurring by chance and those whose occurrences are conditional. These are integrated into a system embodying all scenarios. The risk situation defined is translated into a set of spread-sheet modules over which simulations of project duration are performed. This is done using a general purpose simulation program to evaluate the schedule feasibility. An example design and build project is used to illustrate the proposed approach and highlight the benefits of end-user computing for schedule risk assessment.