# GA-Based Optimization Method for Mobile Crane Repositioning Route Planning
## 1 Introduction  
Cranes are construction equipment that are used to lift loads horizontally or vertically [1]. Cranes have been used extensively as essential equipment in construction because heavy objects are handled frequently at construction sites. Furthermore, as the demand for large-scale construction projects has increased and the benefits of modular construction have been recognized, the use of mobile cranes for lifting and installing large modular materials has also been increasing [2]. Mobile cranes have a built-in motor, which allows it to move to a specific location independently. This makes mobile cranes easier to install, dismantle, and relocate for lifting work compared to tower cranes.  
In modular construction, the mobile crane repeats the task of hanging a load on the hook and transporting it to the installation location. This requires planning, such as selecting an appropriate crane and choosing the crane position while considering productivity and safety. A careful lift plan is required to perform the lifting work successfully. An improper lift plan may lead to high additional costs and schedule delays [2]. Hence, various studies have been conducted to establish optimal lift plans. These studies can be classified into three research themes: (1) optimal mobile crane selection [3; 4; 5; 6], (2) investigation on feasible working areas for mobile cranes [7; 8], and (3) lift path optimization of mobile cranes [9; 10; 11; 12; 13; 14; 15]. As such, many studies have been conducted on mobile crane operation plans. However, very few studies have been conducted to investigate the optimal mobile crane position and travel route.  
A mobile crane can lift loads within the working range determined by the boom length, vehicle size, work safety regulations, etc. [7; 13]. Generally, because the area of a large site is wider than the working range of the mobile crane, the crane cannot be fixed ata certain position and lift loads all over the site. However, it may not be economical to hire and place multiple mobile cranes all over the site. The construction site has a construction schedule according to the construction plan, and the movement of the mobile crane to the appropriate position must be planned to lift loads according to the construction schedule and workload. In this study, we named this problem as the repositioning mobile crane problem (RCP).  
Traditionally, RCP was planned by relying on the intuition and experience of the construction manager or workers. However, to solve RCP, various parameters must be considered simultaneously: the three-dimensional geometry of the construction structure, volume, and shape of the crane, working motions and range of the crane, performance of the crane, workload in each zone, weight of the load, etc. Furthermore, because RCP has a very large solution space, it is difficult to solve based on intuition, and an improper plan can be established easily. In other words, RCP should be solved using a scientific approach, and the development of an integrated system that combines various techniques is required.  
In this study, we propose a method for solving RCP with minimal relocations and in the shortest period. Based on this method, a system named Mobile Crane Reposition route Planning Optimization System (RPOS) was developed. To achieve the goal of this study, the following specific research procedures were performed. First, prior studies on mobile crane operation plans were analyzed to determine the need for a new method to achieve academic and practical progress. Second, the construction site, crane performance, and lift constraints were schematized to model them using numerical data. Third, a genetic algorithm (GA) was used to develop RPOS. Fourth, a case study was conducted to validate the detailed application methods and performance of RPOS.