In this project, the coupling effect exerted by the ballast track in railway bridges and the relevance of its consideration in numerical models was analysed. Likewise, the usual methods of experimental identification of structural damping in both free and forced vibration was critically evaluated. Finally, soil structure interaction effects in short railway bridges was evaluated, with an attempt to detect different interaction phenomena that give rise to a reduction in the structural response. The theoretical results achieved were contrasted with experimental data from test campaigns planned and executed by the researchers.