Buffer Sizing Methods to Compare Critical Chain Project Management with Critical Path

Buffer Sizing Methods to Compare Critical Chain Project Management with Critical Path

Mohammed Shurrab (Department of Mechanical Engineering, Kyushu University, Fukuoka, Japan) and Ghaleb Abbasi (Department of Industrial Engineering, University of Jordan, Amman, Jordan)
DOI: 10.4018/IJITPM.2016070105
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Abstract

Critical Chain Project Management (CCPM) provided a tangible progress to the Project Management Body of Knowledge. The critical chain project management (CCPM) differs from the traditional Critical Path Method (CPM) which includes never changing resource dependencies. CCPM improves the project plan by aggregating uncertainty into buffers at the end of activity paths. In this research, one hundred twenty random projects were generated and analyzed using Microsoft Project software according to the traditional CPM and the CCPM once using the sum of squares (SSQ) method and another using the cut & past (C&PM) method. CCPM-SSQ method revealed an average savings of 13% and 43% in duration and cost, with a standard deviation of 21 and 11 for duration and cost respectively. While the CCPM-C&PM method revealed an average overestimation of about 2% in duration and 43% savings in cost, with a standard deviation of 25 and 11 for duration and cost respectively.
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Introduction

Creation of reliable and accurate schedules in project management is the first step towards project success (Santiago and Magallon, 2009; Kelley, 1963). Using the Critical Path Method (CPM) implies calculating Early Start and Finish dates as well as Late Start and Finish dates by forward and backward analysis of the project network diagram paths. Choosing the relevant resources is usually done after identifying the path. Activity owners add buffers (i.e. safety margin) for each activity in order to overcome the uncertainties (Leach, 2014). Using CPM, if a resource completes an activity before the planned finish date, the time gain is still not propagated to next activity. That is because the early start date of next activity has been not reached yet. However, delays are propagated which may even change the existing critical path (Herroelen, 2001). Critical chain project management (CCPM) is the direct application of the theory of constraints to project management developed by Goldrate (1990; 1997;1998) which is a technique related to scheduling analysis for network that considers task dependencies, scarcity of resources, and buffers.

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