# Scheduling Optimization of Prefabricated Construction Projects by Genetic Algorithm
## 1 Introduction
Some studies have tried to develop an effective assembly-type construction project scheduling method, including mathematical modeling optimization and simulation modeling [19; 20; 21; 22]. However, these previous studies show that the traditional project scheduling technology often ignores the impact of untimely component supply on site construction, or model optimization is usually carried out on the premise of timely and quantitative supply of components. These studies cannot simultaneously consider the two essential construction processes of prefabricated component production and field assembly construction. The project schedule and resource allocation table are often inconsistent with the actual construction demand, and the availability of the schedule is not very high. Although the solution of simulation modeling can fully display the project scheduling process, the workload of simulation modeling is often large, and the solution efficiency is relatively low. This study has developed a prefabricated construction project scheduling optimization model that is more intuitive and easy to solve to make up for the failure to fully consider the impact of the supply of prefabricated components on the scheduling model and the limitations of simulation modeling in the previous research [16; 23]. The model considers the priority and resource occupation constraints of project activities and transforms the constraints of production and transportation of prefabricated components into supply time constraints into the optimization model. The priority relationship between prefabricated construction project activities is complex, and it is constrained by a variety of resources and the supply of prefabricated components. Due to the core genetic operations of the genetic algorithm (including selection, crossover and mutation) will not be greatly affected by project changes. Therefore, this study introduces a GA that is easy to express project-related constraints to solve the prefabricated construction project scheduling problem and designs the genetic operation of GA correspondingly. The study verifies the effectiveness of the algorithm proposed in this paper through experimental calculations on the ProjectScheduling Problem Library (PSPLIB) data set, and then applies the developed model and algorithm to actual prefabricated projects. This study has two important research contributions compared with previous studies that failed to consider the prefabrication characteristics of prefabricated buildings well or use simulation modeling [16; 24]. First, this work provides a prefabricated construction project scheduling optimization model which can consider the supply conditions of prefabricated components. Moreover, this work determines the relevant parameters of the prefabricated construction schedule, such as the delivery time of prefabricated components, resource occupation, and supply restrictions. In contrast with previous studies that ignore the influencing factors of precast components [25], this study can better reflect the actual construction situation of prefabricated buildings and meet the needs of project scheduling arrangements. To a certain extent, it fills the blank that current prefabricated construction project scheduling research results are less or the key factors of the model are not fully considered. Second, in view of the shortcomings of the GA proposed in the past, this research improves the related genetic operation and designs a GA with a stable solution quality, scalability, and high practicability to solve the prefabricated construction project scheduling optimization model. The superiority and practicability of the proposed model and algorithm are verified through experimental calculation, algorithm comparison, and actual engineering case application.