# Large-Scale 3D Multi-Story Enterprise Layout Design in a New Type of Industrial Park in China
## 1 Introduction  
The layout problem in new-type industrial parks is the large-scale 3D multi-story enterprise layout design (3 DMSELD). According to certain principles, the enterprises will be reasonably distributed on all floors of each building in the park. Traditional industrial park layout problems are mainly carried out on a two-dimensional plane [1]. However, intensive production models have become increasingly common with economic development. Many new-type clustered industrial parks have emerged in China and are distributed in the eastern coastal region. These parks generally have multiple multistory buildings leased to dozens of enterprises, which involves the large-scale 3 DMSELD problem. Factory intensification can significantly improve land and infrastructure utilization rates. However, it also creates a concentration of risks. The shortening distance between enterprises has led to a greater possibility of risk interactions. An accident in one enterprise can lead to injury or property damage to others and may even trigger a domino effect [2]. Therefore, it is necessary to consider the risk factors in the park layout problems. With social development, people attach greater importance to safety, and how to reduce risk through layout has become the research focus. Most studies involving safety have considered safety factors as safety costs or constraints. For instance, [PERSON] [3] demonstrated that safety-related costs are relevant for defining optimal layout; [PERSON] [4] treated multiple hazard sources as risk costs in the objective function. However, the safety status of enterprises in clustered industrial parks is closely related, and it is worthwhile to focus on safety factors separately. In particular, [PERSON] [5] argued that it would be inappropriate to turn safety issues into economic numbers in objective functions. The layout problem has been around for a long time; many previous studies have focused onthe single-story layout of a facility [6]. [PERSON] [7] proposed a combined quantitative and qualitative approach to the facilities layout problem on a two-dimensional plane. [PERSON] [8] constructed a model to provide a chemical plant's optimal layout of process equipment. These studies did not solve the three-dimensional layout problem. Research on multi-story layouts has become a hot topic with an increase in multi-story workshops. [PERSON] [9] and [PERSON] [10] presented two 3D models to describe the facility layout problem. However, there are few studies on the three-dimensional optimization layouts at the industrial park level with enterprises as the smallest layout unit. In addition, the park management party's main profit comes from rent affected by the layout. Nevertheless, this has rarely been considered in previous studies. Although significant progress has been made in related fields, we can get some research gaps from the above discussion. First, there is a lack of theoretical research on the large-scale 3 DMSELD problem; Second, researchers have not treated the risk impact between enterprises in much detail; Third, there is a lack of consideration for rental profit in the layout problem. To address the gaps mentioned above, this study used a bi-level integer nonlinear programming (BLINLP) model considering enterprise association risks and rental profit to make hierarchical decisions at the layout stage. First, settled enterprises were divided into risk and non/low risk enterprises. Priority was given to reducing the risk level of the parks. Because the enterprise's inherent risks do not change with location, this study only considered the associated risk between enterprises. For non/low risk enterprises, rents were considered to create enterprise layouts to maximize the park's income. Subsequently, a BLINLP model was presented to solve the large-scale 3 DMSELD problem. To reduce problem size, a specific variable conversion method was proposed. Then, an improved evolutionary algorithm was applied. In addition, a case study was conducted using data from an industrial park in Shunde.