# Track-Bridge Interaction of CWR on Chinese Large-Span Bridge of High-Speed Railway
## 5 Conclusions  
Since 1963, when China first laid a CWR on the Liulie bridge of the Beijing-Guangzhou railway, systematic theoretical and experimental research on the track-bridge interaction has been carried out in China. The track-bridge interaction model is widely used for its strong expansibility and comprehensiveness. Especially in recent years, with the establishment of the theoretical framework of the track-bridge interaction, more and more attention has been paid to this aspect. At present, the development of the track-bridge interaction can be concluded as the following aspects:  
1. The theory of the track-bridge interaction has been developed with the improvement of the theories related to each part of the track and bridge system, which are more consistent with the measured results. Many practical problems of the track on the bridge can be studied by using the finite element model for refinement modeling. In bridge modeling, the finite element method and the modal superposition method are widely used due to their accuracy and efficiency. For some applications, the nonlinear characteristics of the structure can be considered in the beam-return interaction model. \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Load Step Method** & **The Method of** \\
**Load Case** & **Considering Loading** & **Numerical Addition** \\  & **History** & **Numerical Addition** \\ \hline Bending-braking force & 20.5 & 23.0 \\ Braking force + bending force & 20.5 & 23.2 \\ Bending force of rising temperature & 32.2 & 47.3 \\ Expansion force + bending force & 37.2 & 47.3 \\ Bending force of lowering temperature & 49.1 & 31.1 \\ \(-\) Expansion force + bending force & 58.3 & 47.3 \\ Bending-braking force of rising temperature & 32.6 & 51.5 \\ Expansion force + bending force + braking force & 37.0 & 64.2 \\ Bending-braking force of lowering temperature & 48.7 & 41.4 \\ \(-\) Expansion force + bending force + braking force & 67.3 & 44.2 \\ \hline \hline \end{tabular} Note: for the convenience of comparison, the load method is also used to calculate the bending force and braking force separately.  
\end{table} 
Table 2: Extreme values of rail longitudinal force considering loading history (unit: MPa). 2. The track-bridge interaction has shown its advantages in various engineering applications. For a large-span bridge of a high-speed railway under design or in service, it has become a common practice to evaluate the bridge by using the track-bridge interaction. Through the stress analysis of the track-bridge system, the actual service condition of the bridge can be better described, and the fatigue life assessment of the bridge can be more reliable. The longitudinal force of the rails of the five large-span railway bridges mentioned in the paper is obviously larger than that of the medium- and small-span railway bridges. Therefore, to control the force and deformation of the system, the rail expansion regulator, viscous damper, speed lock, small resistance fastener, or the support type and section type can be changed according to the actual situation. 3. Considering the loading history, the track-bridge interaction theory is more refined, which makes the calculation results more consistent with the measured results. With the development of experimental methods and statistics, seismic science, wind engineering, and other related disciplines, system excitation can be described with high precision by measured data or more and more accurate models, and numerical algorithms also show strong large-scale computing ability. It can be used to evaluate the safety of the track-bridge system under special excitations such as earthquake load, complex temperature load, shrinkage and creep load, and multiple-load superposition. Conceptualization, B.Y. and W.K. ; methodology, B.Y., W.K. and R.G. ; search and analysis, B.Y., W.K. and H.X. ; writing--original draft preparation, B.Y. and J.H. ; writing--review and editing, W.K. and R.G. ; supervision, W.K. and H.X. All authors have read and agreed to the published version of the manuscript.