On the vertical coupling effect of ballasted tracks in multi–span simply–supported railway bridges under operating conditions

This contribution investigates the vertical coupling exerted by ballasted tracks on the vertical response of bridges composed either of (i) several successive simply-supported spans with weak coupling between them due to the continuous track; or (ii) adjacent single-track decks conforming a double-track bridge, in which interaction effects are induced due to the transverse continuity of the ballast layer. To this end, 2 D and 3 D track-bridge interaction Finite Element models are implemented, which consider a three-layer discrete and explicit idealization of the track. The 2 D track-bridge interaction model is used to perform sensitivity analyses on the track parameters, which have revealed that the ballast shear mechanisms along the track may significantly affect the train-induced vibrations under resonant conditions. Then, the influence of the ballast coupling on the response of twin adjacent decks is investigated with a 3 D track-bridge interaction model. To this end, this model is updated based on the results of an experimental campaign performed on a real bridge composed of two SS spans and two single track twin adjacent decks. The numerical-experimental comparison shows an evident dynamic vertical coupling between the bridge decks and reveals the importance of including the ballasted track in the modelling process of these structures.