Scheduling in construction is complex. Before an activity can be conducted, a number of preconditions first have to be fulfilled. In Last Planner System this removal of constraints is referred to as the making ready process. To ensure that this process is running, the preconditions need to be known. Therefore, in an attempt to bring these preconditions into light three construction projects have been followed. Here reasons for non-completed activities have been collected. In total 5014 activities have been registered whereof 1279 was not completed according to schedule. Afterwards the non-completed activities were sorted into nine main categories. The six of the categories are basically corresponding to the ones presented by Koskela (1999), while the last three are an expansion of Koskela’s external condition category. The preconditions are as follows: 1) Construction design and management. 2) Components and materials are present. 3) Workers are present. 4) Equipment and machinery are present. 5) Sufficient space for conduction. 6) Previous activities must be completed. 7) Climate conditions must be in order. 8) Safe working conditions in relation to national “Health and Safety at Work Act” have to be present, 9) Known working conditions. Often a problem during excavations or refurbishment assignments where existing conditions first has to be examined. One of the major and underlying reasons to non-completed task is insufficient and even bad scheduling. Often non-sound and out of sequence activities are selected to the Weekly Work Plans. When conducting the schedule it is important to notice as described in Lindhard and Wandahl (2011) that the soundness of an activity can vary over time. By focusing on all nine preconditions a more robust schedule can be achieved. A more robust schedule induces an increased percent planned completed level and moreover and increased productivity.
Lean Construction, Preconditions, Constraints, Last Planner System, Making Ready,
Lindhard, S. & Wandahl, S. 2012, 'Improving the Making Ready Process - Exploring the Preconditions To Work Tasks in Construction' In:, Tommelein, I.D. & Pasquire, C.L., 20th Annual Conference of the International Group for Lean Construction. San Diego, USA, 18-20 Jul 2012.