Numerical analysis of track: structure interaction and time domain resonance

This paper illustrates the mechanics of track-structure interaction and resonance, and the finite-element (FE) modelling of railway girders subjected to combined live and thermal loadings. The numerical analysis makes use of the recent insertion of a ballast FE into the FE code FIBRE. The element complies with the Italian railway specifications and has been tested and validated accordingly. The program, originally developed to model the seismic (dynamic) response of civil structures, can perform step-by-step non-linear analyses in the time domain using a state-of-the-art library of fibre beam-column elements and other bridge dedicated FEs Such as frictional bearing, gap, tendons, etc. Following the implementation of the ballast element, the non-linear static and dynamic responses of railway bridges can be analysed considering the track-structure interaction effects. With the same FE mesh, temperature effects, quasi-static, and dynamic (resonant) response under live loading as well as seismic response of bridge structures can now be analysed with a unified approach. In all these cases, the continuous welded rail significantly modifies the response of railway bridges, especially in the small to medium span range. After discussing the new ballast FE, a numerical case study is presented showing all the different types of analyses that can be performed with the program. The principal mechanisms governing the response of railway girders and bridges are discussed showing the stress-strain time histories of the principal bridge elements.