# Current Practices of Railway Ballastless Track Design Methods in China
## 5 Conclusions  
Based on the methodological analysis of the LSM and the ASM, the reinforcement and structural design of a prefabricated slab track are analyzed and computed by combining finite element analysis and formula calculation. Simultaneously, the differences between the two methods and the influencing factors are explored. Furthermore, the material-saving effect and control parameters of the LSM in structural design are studied, which engendered the future development directions and suggestions for optimizing the structural design method. The main conclusions are as follows:  
1. For a single load, the load values of the ASM and LSM are basically similar, but for train loads, the value of the ASM is more conservative than the LSM. Therefore, the vertical train load effect of the ASM has a significant margin compared with LSM and is greatly affected by the working conditions. There is not much difference in the effects of other loads under the two design methods. Figure 15: Required thickness of track slab under different working conditions. (**a**) D1. (**b**) D2. (**c**) D3. 2. In terms of combination values of the load effect, the main force combination of the ASM is larger than that of different combination methods of the LSM, in which the fundamental combination plays a control role. Among various factors, working conditions have little influence on the combination values of effects. With the increase in the temperature gradient, the combination values under the two design methods all grow linearly, which means that the temperature gradient plays an important role. In areas with large temperature fluctuations, the temperature load will be the main controlling factor of structural effects. 3. In terms of reinforcement, the calculation processes are different between the two design methods. For the ASM, stress and cracking are checked according to the main force combination in calculation of the reinforcement ratio. For the LSM, the stress is calculated according to the fundamental combination or accidental combination, and cracking is checked according to the standard combination. The results show that reinforcement according to the LSM can save materials on the premise of meeting the specification requirements, by nearly 6.5%. The results are mainly controlled by the temperature gradient. Similarly, under a certain amount of reinforcement, the slab thickness of the LSM can be approximately 3.4% less than that of the ASM, which is also predominantly controlled by the temperature gradient. However, because the partial coefficients of the current LSM specification in China are calibrated according to the ASM, the optimization effect of the LSM in track design is not so significant, and theoretical advantages of probability-based design of the LSM in international standards cannot be fully leveraged. 4. The rational coefficient values of the LSM remain to be studied further to meet the future requirements of structural design. In particular, appropriately accounting for temperature effects is vital because of its significant influence on track structure design under large temperature variations compared to other factors. Since 2011, railway track design in China has transitioned from the ASM to the LSM, and a series of scientific research projects have been carried out. In 2018, the Code for the Design of Railway Tracks (Limit State Method) (Q/CR 9130-2018) [31] was published. During the formal transition process, due to limited time, basic data, working conditions and other resource, in-depth research on the expression and important design parameters such as the partial coefficients was lacking. In particular, the values of correlation coefficients were calibrated based on the ASM, which caused a restricted optimization effect. The LSM has great room for improvement in design redundancy reduction and material efficient utilization using scientific parameter values.