# Current Practices of Railway Ballastless Track Design Methods in China
## 1 Introduction
In terms of track design theories and methods, they have gone through a lengthy developmental trajectory, and two mainstream methods emerged: the allowable stress method (ASM) and the limit state method (LSM). Since the mid-19 th century, to ensure the  
Figure 1: Different track structures in China. safety and reliability of railway infrastructure, the ASM has been used in structural analysis and design at the stage of material elasticity [17]. This method is based on linear elasticity theory, and the calculation is very simple and convenient [18; 19]. In China, based on the allowable stress method, the Code for the Design of Railway Tracks (TB10082-2017) [20] specifies the design loads and load effect of tracks and guides the structure design of ballastless tracks in earlier times. However, due to the adoption of a single empirical safety factor [21], the ASM cannot maintain a consistent safety level for various structures [22; 23]. At the same time, it also has a large design margin for design of track structure, which leads to the waste of materials [24]. So, there is still room for optimization and perfection. With the improvement in structural reliability theory, the LSM based on probability theory has begun to develop gradually [25; 26]. International standards such as the Analysis and Design of Reinforced and Prestressed Concrete Guideway Structure (ACI 358.1R-92) [27] began to use reliability methods as the basis for safety analysis [28]. The LSM was also used in the design of railway track gradually. [PERSON] et al. [29; 30] found that the LSM can give full play to the fracture toughness of structures, which can reduce the material cost of each railway by 15%. However, compared with European and American countries, Chinese railway system reliability research started later. To adapt to more refined design, by learning from successful cases of foreign specifications, relevant design specifications of China were officially promulgated in 2018 [31]. Based on the LSM, many domestic scholars proceeded with optimization research on existing track structures. [PERSON] [32] et al. compared and analyzed the reinforcement results of the LSM and the allowable stress method for various track of the CRTS and put forward some suggestions. Based on the LSM, [PERSON] [33] et al. checked and optimized CRTS I slab track structures. The results indicated that the existing structure met ultimate and serviceability limit state requirements, and the optimization could greatly save reinforcement. Thesis research laid the foundation for the promotion and application of the LSM in ballastless track design. In recent years, the LSM has gradually been applied, but the current structure design of the ballastless track is still in the transition period of specification, and the two design methods are used concurrently. In addition, most of the studies focus on using the LSM for checking existing structures, which have been reinforced according to the ASM. There is still a lack of research that specifically analyzes the optimization effects of the LSM in track design and its main influence factor compared to the ASM. Therefore, deeper analysis of track design methods is necessary. By systematically summarizing the fundamental principles, the primary distinctions between the LSM and the ASM are indicated. Taking a new prefabricated track of an express railway as an example, the difference of calculation process, design results and parameter influence rules of the two design methods are analyzed, combining finite element method with formula calculation. Consequently, the optimization effects and control parameters of the LSM compared to the ASM in structural design are explored. Furthermore, the development directions and suggestions for improving the structural design methodology are proposed, which provides reference for the design of new structures.