Enhancements to Methods for Planning and Scheduling Fabrication Projects Utilizing Multiskilled Labour Resources
Creators: Zahedi, Leila
Publisher: name: University of Alberta Library
Year: 2023

<p>In prefabrication and off-site construction, various multiskilled work crews need to be assembled to work on different workstations to process custom-designed work units, each having specific requirements for material handling, assembly connections, welding, etc. However, the frequent labour transfers between different workspaces and the labour waiting time for forming crews at particular workstations result in non-value-adding efforts, which can cause operation interruptions and loss of efficiency. This phenomenon of dynamic formation of crews and labour movement between different workstations cannot be adequately addressed by the current approach to planning and scheduling of prefabrication construction projects due to the inherent limitations in the established planning and scheduling methods and tools. Accordingly, the labour-cost estimate derived from mainstream project scheduling software (such as Microsoft Project and Primavera P6) has largely overlooked such inefficiency stemming from dynamic labour resource transferring and crew formation between activities in the operations of prefabrication and off-site construction. Despite numerous efforts aimed at enhancing current methods in project planning, scheduling, and budgeting, there have been limited studies attempting to model the efficiency of multiskilled labour flows between different project activities. As a result, a lack of quantitative modeling was identified to understand the efficiency of labour flow at the activity level and its impact on project outcomes, particularly on project scheduling and budgeting.<br>
This research aims to bridge the gap in knowledge and practice in planning, scheduling, and budgeting prefabrication projects by integrating current project scheduling practices with productivity measurements. The proposed research extends the theory and application of the Critical Path Method (CPM)-based project planning and scheduling. It introduces a practical discrete-event-simulation-based framework to model the labour utilization efficiency in connection with multiskilling and dynamic crew formations in prefabrication and off-site construction, resulting in the generation of more accurate labour cost estimate and budget (S-curve). The framework provides a basis for further analysis of labour productivity and lean construction performances, enabling potential performance improvement and labour utilization optimization in the project planning stage.<br>
In current practice of prefabrication and off-site construction featuring frequent labour transferring between different workstations in the finite dynamic shop space, precisely measuring the efficiency of labour transferring between different workstations is prohibitively expensive and practically unacceptable due to privacy infringement and ethics challenges. Hence, collecting actual job cost data to differentiate the labour time spent in crew formations and labour movement between different workstations from the productive labour time is deemed infeasible in practice. In this study, planning steel girder fabrication projects subject to resource availability and transfer constraints are modeled by a simulation methodology in order to logically represent project execution processes in sufficient details, while enabling quantitative analysis of crew formations and labour transfer times. <br>
A new time-dependent utilization efficiency factor, called the inter-activity resource utilization efficiency factor, is defined to quantify the efficiency of crew formations and labour resource transfers between different workstations at each point of time during the project time span. The derived efficiency factor is then factored into the budgeted labour-hours S-curve to generate a more accurate labour cost estimate of a construction-oriented fabrication facility. The simulation results demonstrate that by properly allocating multiskilled labour resources and fine-tuning crew size, the efficiency of labour transfers between different workstations can be significantly improved, thereby giving rise to better time and cost performance for the entire project.<br>
Further, the analytical formulation of the optimization problem is also attempted by applying Integer Programming, aimed at minimizing the labour flow and crew formations inefficiency. As demonstrated in the research, the resulting optimized solution is expected to significantly decrease Labour Flow Waste Index by utilizing Microsoft Excel Solver on small-size demonstration cases or applying established evolutionary optimization algorithms to scheduling simulation models for large-size realistic cases. The proposed methodology is verified and validated through collaboration with a steel fabricator in Edmonton, Alberta.</p>