A Full 3D Railroad System Model to Investigate Train-Substructure Interaction Under Dynamic Load

Since the first day the railroad have been invented, it has become one of the most important methods of transportation for both passengers and goods. Millions of miles of railroads tracks are crossing the land all over the world to facilitate the transportation of passengers and different products. The importance of the railroad raised the interest of many researchers and engineers to try to understand and improve the performance of the rails. The finite element method (FEM) has been used widely, as a very powerful numerical method, in the literature to model and investigate the performance of the different components of the railroad system. A lot of scientists used the FEM to study different issues associated with the railroad system, such as stresses in the wheel or the rail web, degradation of the ballast, soil settlement, and many other problems. Beside the FEM, the multi-body systems dynamics (MBS) have been used by many researchers as well as the FEM in the same field. It is very useful tool especially when it comes to the dynamic analysis and investigating the vehicle performance or issues related to the wheel/rail contact. In this work, a detailed model that couples both FEM and MBS in one model is created. This model consists of a full 3D FE model that includes the different components of the railroad system (rails, sleepers, ballast, subballast, subgrade, and fasteners) using beam, solid and spring elements. The FE model is then coupled with the MBS code to extract the output of the dynamic analysis. The model was verified with the results in the literature and showed great performance. The good results of the coupled model provided a strong motivation to move forward with another problem, which is the bridge approach problem in this work. A new coupled model was created to investigate the bridge approach problem that arises from the variation of the stiffness below the rail due to the stiff foundation on the bridge and the softer substructure before and after the bridge. To solve the stiffness variation problem, a concrete slab was implemented under the ballast before the bridge with one end resting on the abutment. Two designs of the slab were studied in this work, namely rectangular and inclined slab. The performance of both slabs was compared with the no slab case, and the results showed great improvement in the vertical displacement, the contact force, and the substructure stresses for both slabs, while the inclined slab showed better performance than the rectangular one as it provides a gradual change in the stiffness in the approach zone. The results of this work show the effectiveness of the presented coupling technique between the FEM and MBS in one model and the usefulness of the presented models. The bridge model analysis showed the effectiveness of the inclined slab as a recommended solution for the approach zone problem and its impact on the reduction of the vertical displacement, the contact forces, and the stresses.