A novel mathematical optimisation model for the scheduling of activities in modular construction factories

Modular construction has been reported to lead to a number of advantages when contrasted with conventional construction approaches, including time and cost savings, along with reduced environmental impacts. Given that the operations involved in modular construction take place within a controlled environment, an integral factor that impacts the productivity of works involved is the timely scheduling of the associated activities. Unlike conventional on-site construction methods, operations in modular construction take place in a sequential and linear manner, with large dependence on adequate resource allocation to specific workstations. In a bid to address the lack of mathematical optimisation methods that target the scheduling of operations in a modular factory setting, this paper proposes a novel mixed integer non-linear programming model for optimising the scheduling of modular construction activities on the shop floor of modular factories. The impact of scheduling of resources, such as overhead cranes, and the distance between stations to which activities are scheduled are factored in the proposed method. The solution approach presented for solving the scheduling problem involves the linearisation of the model to enable the use of efficient off-the-shelf solvers. A realistic case study is implemented, and an extensive computational experiment is also conducted to test the robustness and tractability of the proposed method. The performance of the model is also contrasted with a commonly adopted heuristic, with the model producing project durations reductions that are 43% less than that of the heuristic.