ANALYSIS OF THE INFLUENCE OF THE BALLAST TRACK IN THE DYNAMIC BEHAVIOUR OF SINGLE-TRACK RAILWAY BRIDGES OF DIFFERENT TYPOLOGIES

Abstract. In the present contribution the coupling effect of the railway track on the dynamic response of single-track bridges with several simply-supported spans is investigated. The response of such structures is of interest due to the possible appearance of high vertical accelerations at the platform, with adverse consequences such as ballast deconsolidation, loss of track stability etc., especially at resonance. Single track railway bridges due to their inherent low mass and damping, are especially critical in this regard.This paper provides a detailed sensitivity analysis over a single track railway bridge catalogue considering lengths of interest from 10 to 25 meters with different typologies: concrete filler beam and concrete slab decks, taking into account and neglecting the vertical flexibility of elastic bearings. To this end, a 2D Finite Element numerical model is implemented admitting a three-layer discrete representation of the track components mass, stiffness and damping, based on [1].The effect of the track on the bridge acceleration response is evaluated. A parametric analysis is presented with the aims of (i) detecting the track parameters that affect the most the bridge vertical acceleration response under railway traffic and (ii) determining what bridges are the most affected by the rigidity and the damping induced by the track components. Additionally, the effect of including several isostatic spans in the model is also evaluated with the goal of concluding where the maximum response occurs and what models are on the safe side.In addition, the experimental response of a real two-span railway bridge belonging to the Spanish railway conventional network is presented under operating conditions. The bridge modal properties identified in a previous work by the authors [2] are employed and the previously described numerical model is calibrated and used to simulate the structural response under railway traffic.Finally, preliminary conclusions are extracted regarding the coupling effect of the track components both at resonant and not resonant conditions.