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.
Appears in: EDULEARN21 Proceedings Publication year: 2021Pages: 1000-1006ISBN: 978-84-09-31267-2ISSN: 2340-1117doi: 10.21125/edulearn.2021.0259Conference name: 13th International Conference on Education and New Learning TechnologiesDates: 5-6 July, 2021Location: Online Conference
Modular steel bridges are structures whose construction is based on regular prefabricated truss units. This presents several advantages, such as rapid and easy deployment, high adaptability to the terrain and reduced construction costs. However, they generally face operational restrictions for span lengths greater than 60m. Recent technological innovations search to overcome these limitations and develop modular structures with larger spans. Hence, the main objective of this work is to evaluate the dynamic effects on long-span modular steel bridges. The present contribution provides a study on two modular bridge typologies, considering different span lengths from 120 to 140m. A 3D coupled vehicle–bridge model is used to analyse the vehicle–bridge interaction and the dynamic load allowance of the structures. The vehicle is represented as a multibody truck system and the bridges are modelled with the finite element method. Several types of randomly-generated road irregularities are considered on the bridge deck. The effect of each type of irregularity is evaluated on the dynamic load allowance of the bridges. The results obtained reveal the notable influence of road irregularities that involve abrupt vertical displacements that excite the vehicle mode shapes. In addition, it is observed that dynamic load allowance indices tend to decrease with longer spans and higher speeds, except when a resonance is produced.
The dynamic response of railway bridges can be highly influenced by the effect of soil–structure interaction. This occurs as the soil dissipates energy and modifies the flexibility of the bridge supports, which impacts the modal parameters of the structure and its response to passing trains. In the case of partially-buried structures such as portal frames, this interaction mechanism is of particular relevance. However, simulating the soil effect is complex, and may require an elevated computational effort. Under these conditions, obtaining accurate predictions of the bridge dynamic behaviour becomes challenging. For this reason, the interplay between the bridge and the soil is usually disregarded. To address this limitation, a numerical approach devoted to implement soil–structure interaction with reduced computational cost is presented in this contribution. The method is based on a substructuring scheme, and considers two numerical models: (i) a full three-dimensional finite-element interaction model, including the track, the bridge, and the surrounding soil, and (ii) a simplified version of it, in which the soil is substituted by a series of linear spring-dampers. The first model is used to derive frequency-dependent dynamic stiffness functions that describe the mechanical coupling between the bridge and the ground. Then, these functions are used to calibrate the spring-damper elements representing the soil in the subsequent simplified model, and the dynamic problem is solved by complex modal superposition. The suitability of the proposed methodology is evaluated through its application to an existing portal frame railway bridge. The effect of other relevant aspects on the bridge response such as the track irregularities and the contribution of the vehicle–bridge interaction is also taken into account. The results highlight the potential of this approach to obtain satisfactory predictions of the bridge performance in an efficient manner.
