Mechanistic analysis of concrete crosstie and fastening system using field-validated finite element model

The objective of this dissertation is to further investigate the performance of concrete crosstie and fastening system under vertical and lateral wheel load using finite element analysis, and explore possible improvement for current track design standard. The damage of fastening system is one of the most prevalent failure causes for concrete crosstie track, however the current AREMA design standard only includes evaluative tests for the fastening system, rather than a mechanistic design approach. To improve the current design approach, the vertical and lateral load path through the track structure and the component demand within the concrete crosstie and fastening system should be further investigated. In addition, to facilitate the application of the knowledge related to the load path through the concrete crosstie and fastening system, mechanistic models should be developed so that engineers could easily estimate the distribution of wheel load. The research work presented in this dissertation includes the following tasks: 1) developing a detailed finite element model of the prestressed concrete crosstie and fastening system based on the manufacturer's design, 2) validating the component models of the rail clip and the prestressed concrete crosstie based on manufacturer's information and crosstie flexural test, 3) validating the single-crosstie-fastening-system model based on laboratory experimentation, 4) validating the multiple crosstie model based on the field experimentation conducted on instrumented track, 5) validating the multiple crosstie model based on full-scale laboratory experimentation under asymmetric loading scenarios, 6) using the validated FE model to conduct parametric studies about the failure mechanisms of the concrete crosstie and fastening system, and the effect of critical design parameters on the performance of the track structure, 7) developing a mechanistic model to estimate the distribution of lateral wheel load and the rail head lateral deflection based on the design of the track structure and the loading scenario, and 8) using the proposed mechanistic model to develop a simplified design tool based on Microsoft Excel so that railroad track engineers can use the mechanistic model to efficiently determine the track response. Based on the model validation at different levels, it is proven that the detailed finite element model is able to capture some critical mechanisms of the track structure including the rotation of the rail, the response of the fastening system, the distribution of wheel loads and the flexure of concrete crosstie. In addition, the field validation of the finite element model and the parametric studies provide some valuable insights on the load path and performance of the continuous track structure.