Panel Stacking and Worker Assignment Problems in Residential Construction Using Prefabricated Panels: A Lean Approach
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A current trend in residential construction is the use of prefabricated wall panels. It is important to carefully establish how panels will be stacked, because an optimal sequence will improve productivity and reduce the possibility of worker injury. Mathematical models and heuristics are proposed for solving the panel stacking problem without consideration of interference. Dissertation work includes a mathematical model of the corresponding panel stacking problems in which the goal is to minimize total weighted panel move distance concurrent with certain construction assumptions. The heuristic method was provided to establish how each panel would be stacked and gave the drop-off location of each stack. The heuristic method was found to be able to reduce the total weighted panel move distance and ensure connectivity was always maintained, meanwhile, interference could also be avoided. In terms of solution speed, the heuristic method can solve real size problems in less than one second. Solutions to such problems can increase productivity. Three improvements to the only known existing panel stacking algorithm with consideration of interference were proposed. The computational results indicate the proposed algorithm performed better than existing algorithm in all experimental cases. Improvement on panel move distance ranged from 1.35-47.93%, and improvement on interfering panels ranged from 20-100%. The proposed algorithm can solve non-rectangular cases (not possible with existing algorithm) and was compared with an experienced panel designer and commercial software. When compared to the proposed algorithm, total weighted panel move distance increased 0.10-85.52% and 0.77-136.23%, respectively, for the panel designer and software. While connectivity was 100% for all cases with the proposed algorithm (the algorithm ensures connectivity is always maintained), it ranged from 69.56-86.95% and 73.33-90.91%, however, for the panel designer and software respectively. Finally, the proposed algorithm can solve the interfering panels in the last stack: this cannot be done with the existing algorithm. Because prefabricated wall panels are typically large and cumbersome to work with, there is a significant probability of worker injury. It is important to carefully establish how each panel will be handled by workers. This is typically the responsibility of field construction foreman, but such personnel are often ill-equipped to make such decisions. An alternative, proactive approach is to establish how each panel will be handled in advance, such that overall ergonomic consequences can be properly considered. This dissertation presents mathematical models of the corresponding construction task scheduling and worker assignment problems, where the goal is to minimize total project completion time (subject to worker quantity constraints) and assign tasks to workers as evenly as possible. The solution of such problems can help residential construction managers better plan construction by establishing the ergonomic impact associated with a given construction plan. A heuristic was also developed to solve large problems by balancing workload between workers. The heuristic was found to be able to provide near-optimal solutions, and can solve large problems in less than one second.
- Doctoral Dissertations