Critical path method with multiple calendars

This paper presents the critical path method forward and backward passes with multiple calendars. Multiple calendars are required in many construction projects to effectively represent various project conditions such as work properties, resource availabilities, weather conditions, etc. For this reason, major project management software packages such as P3 and MS-Project provide functions to handle multiple calendars. However, the background theory of handling multiple calendars has not been disclosed, so users of those software packages simply assume without clear knowledge that the time data generated by them are correct. This paper provides how multiple calendars should be handled in scheduling. Applying the theory presented herein, it has been noticed that the P3 operations with two calendars may generate a wrong answer for a start-to-finish with zero lag and inconsistent results in all negative lags when nonworking days are involved. The theory covers all four relationships in the precedence diagramming method with lags of zero, positive, and negative values. This study should be of considerable benefit to the construction industry and academics because it details and advances the theory for scheduling with multiple calendars, which is real scheduling in practice.