Construction Scheduling using Critical Path Analysis with Separate Time Segments
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Project managers today rely on scheduling tools based on the Critical Path Method (CPM) to determine the overall project duration and the activities’ float times. Such data provide important information about the degree of flexibility with respect to the project schedule as well as the critical and noncritical activities, which leads to greater efficiency in planning and control of projects. While CPM has been useful for scheduling construction projects, years of practice and research have highlighted a number of serious drawbacks that limit its use as a decision support tool. The traditional representation of CPM lacks the ability to clearly record and represent detailed as-built information such as slow/fast progress and complete representation of work interruptions caused by the various parties involved. In addition, CPM is based on two unrealistic assumptions: that the project deadline is not restricted and that resources are unlimited. With CPM, therefore, the most cost-effective corrective actions needed in order to recover delays and overruns cannot be determined. This research is based on the view that many of the drawbacks of CPM stem from the rough level of detail at which progress data is represented and analyzed, where activities’ durations are considered as continuous blocks of time. To overcome CPM drawbacks, this research presents a new Critical Path Segments (CPS) mechanism, with its mathematical formulation, that offers a finer level of granularity by decomposing the duration of each activity into separate time segments. The CPS mechanism addresses the problems with CPM in three innovative ways: (1) the duration of an activity is represented as a series of separate time segments; (2) the representation of the progress of an activity is enhanced; and (3) an optimization mechanism to incorporate project constraints into the CPS analysis. To demonstrate the ability of the CPS to provide better analysis than the traditional CPM, a number of case studies are used to show its ability to (1) simplify network relationships and accurately calculate floats and critical path(s); (2) achieve better resource allocation and facilitate accurate delay analysis; and (3) overcome problems associated with the use of multiple resource calendars. This research represents a change from well-known CPM techniques and has the potential to revolutionize and simplify the analysis of ongoing and as-built schedules. The developed CPS technique is expected to help project managers achieve a better level of control over projects and their corrective actions because it offers better visualization, optimization, and decision support for meeting project goals within the specified constraints.