The Effect of Critical Activity on Critical Path and Project Duration in Precedence Diagram Method
The additional relationships i.e., start-to-start, finish-to-finish, and start-to-finish, between activity in Precedence Diagram Method (PDM) provides a more flexible schedule than traditional Critical Path Method (CPM). But, changing the duration of critical activities in the PDM network will have an anomalous effect on the critical path and the project completion date. In this study, we classified the critical activities in two groups i.e., 1. activity on single critical path and 2. activity on multi-critical paths, and six classes i.e., normal, reverse, neutral, perverse, decrease-reverse and increase-normal, based on their effects on project duration in PDM. Furthermore, we determined the maximum float of time by which the duration each type of critical activities can be changed without effecting the project duration. This study would help the project manager to clearly understand the behavior of each critical activity on critical path, and he/she would be able to change the project duration by shortening or lengthening activities based on project budget and project deadline.
 H. N. Ahuja, Project Management-Techniques in Planning and Controlling Construction Project, 2nd ed., John Wiley & Sons, New York, 1994.
 J. W. Fondahl, “A non-computer approach to the critical path method for the construction industry,” J. Constr. Eng. Manage., vol. 132 no. 7, pp. 697-711, 1961.
 J. D. Wiest, “Precedence diagramming method: Some unusual characteristics and their implications for project managers,” J. of Operations Manage., vol. 1, no. 3, pp. 121–130, Feb. 1981.
 D. J. Wiest and K. F. Levy, A Management Guide to PERT/CPM with GERT/DCPM and other Networks, 2nd ed., Prentice-Hall, Inc., USA, 1977.
 M. Lu and H. C. Lam, “Transform Schemes Applied on Non-Finish-to-Start Logical Relationships in Project Network Diagrams,” J. Constr. Eng. Manage., vol. 135, no. 9, pp. 863-873, Sep., 2009.
 J.J. Moder, C.R. Phillips and E.W. Davis, Project Management with CPM, PERT and Precedence Diagramming, 3th ed., Van Nostrand Reinhold, USA, 1983.
 S. Mubarak, Construction project Scheduling and Control, 2nd ed., John Wiley & Sons, Canada, 2008.