Ballast shear effects on the dynamic response of railway bridges

Single-track railway bridges are susceptible of experiencing high levels of vertical acceleration on the deck that may be dangerously accentuated at resonance. This is especially critical for short-to-medium span simply supported bridges. This problem can compromise the safety of the trains and increase the maintenance costs of the track. The main objective of this work is to investigate the influence of the ballasted track on the dynamic behaviour of these structures. The present contribution provides a detailed sensitivity analysis over a wide single-track bridge catalogue covering span lengths from 10 to 25 m and considering two common deck structural typologies: girder-deck and slab-deck bridges. The effect of the vertical stiffness of the neoprene bearings is also evaluated. A 2D Finite-Element track–bridge interaction model is implemented and used to analyse the effect of the track on the modal parameters, harmonic response and vertical acceleration of the bridges under train passages. Additionally, the weak coupling exerted by the track is studied for structures with an increasing number of consecutive spans. The results obtained reveal a notable influence of the mobilised ballast shear transfer mechanism on the dynamic response of the structures, especially for the shortest girder bridges. Finally, a track–bridge interaction model of an existing short girder bridge from a conventional railway line is updated and used to predict the experimental response measured under operating conditions. The adequacy of the numerical tool and influence of the ballast shear parameters on the dynamic response are shown.