This paper discusses the dynamic behavior of twin-box girder bridges under high-speed railway traffic. On the basis of several representative examples derived from recently built high-speed bridges, this contribution examines the effects of transverse bending in the upper slab of these structures and evaluates the bending moments in resonance conditions. The analysis was carried out according to one of the reference norms for the assessment of dynamic effects in high-speed bridges (Eurocode). The results demonstrate that the predicted dynamic response for shorter-span bridges can be unexpectedly higher than the static effects caused by the design loads as a result of transverse resonances induced by the absence of transverse diaphragms between the box girders and the movement of the sliding supports. Moreover, these strong impact coefficients may occur even when the maximum level of vertical vibrations in the deck is not severe.
In this contribution the authors include results and conclusions from an experimental and numerical analysis of a railway bridge belonging to the Madrid-Sevilla High-Speed railway line in Spain. This structure is monitored due to its short length and typology, which make it susceptible to experience high transverse vibration levels. During the in-situ tests the soil properties at the site were obtained. Also, the response of the structure under the circulation of railway convoys was measured at several points of the deck and at the abutments. From the experimental measurements the modal parameters of the bridge are identified. Finally the experimental results are compared to those provided by a finite element numerical model in the time and frequency domains. Conclusions are extracted regarding the structure performance and the adequacy of the numerical model implemented.
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.
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.
This paper contributes to comprehend the vertical vibrational response of oblique, simply-supported girder bridges on high-speed railway lines. Simplified methods adopted for dynamic analysis of such structures admit 2D beam-type models for the assessment of the Serviceability Limit State associated to traffic safety. However, in skewed bridges with multi-track decks and open sections, the dynamic response under railway loads is rather complex due to the coupled participation of three-dimensional modes. Based on experimental data from two existing bridges of different span lengths, detailed digital twins which include an explicit representation of the ballast track are implemented. Taking these models as reference, the influence of skewness on the modal parameters and maximum acceleration under passing trains is evaluated considering bridge variants. Correlation with the presence of transverse diaphragms at the supports and the restraining effect of the ballast track between spans is investigated as well. Finally, the adequacy of considering vehicle-bridge-interaction effects is assessed through numerical-experimental comparisons. The results reveal a reduction in maximum acceleration levels with increasing skewness and a notably weak coupling between consecutive spans, suggesting that classical single-span models may not always safely estimate the deck's maximum vertical response.
