MS9.5 - Dynamics of Railway infrastructures

The High-Speed Rail (HSR) is a complex system involving numerous technical aspects such as operations, infrastructure, and rolling stock. Among the most used infrastructures, bridges play a crucial role in allowing the railway to connect regions without interruption. Although the HSR's increased running speed reduces travel time and costs, safety and comfort should not be overlooked and must remain a primary goal. Because running trains cause large vibrations in substructures while also impacting train performance through the dynamic actions of track and bridge, understanding the train-track-bridge system has been a major focus of recent research. All of these are fundamental for the continuous development of the HSR, aiming at the preservation of the structural integrity of the bridge's operational safety. However, it is observed that the current models available in the literature are unable to introduce multiple interfaces of the train-bridge system at the same time, such as wheel-rail interaction, track-bridge interaction, and soil-structure interaction. Then, given the importance of high-speed rail for future transportation development, this work aims to close this gap by introducing a fully integrated three-dimensional train-bridge dynamic model, thereby opening a new door in the dynamic analysis of such systems. The model was developed through the interaction between the Matlab® and ANSYS® (2022) FEM platforms. The former allows for interaction between the bridge soil and the vehicle model, whereas the second takes advantage of existing modeling capabilities and solvers to consider any generic TBI and SSI scenario. A wheel-rail interaction element was created to simulate wheel-rail contact, to assess structure behavior at any level of complexity, including systems with significant nonlinearities. The normal contact was developed using a Hertzian formulation, whereas the tangential was created using various creep force theories.

The infrastructure manager (IM) DB Netz AG (Germany) is responsible for a safe infrastructure under the traffic operated. The infrastructure is on average 80 years old and designed for the traffic and the respective load models known at the time of construction. Traffic changes, not in the maximum axle loads 22.5 t in passenger traffic), but in the utilisation of the permissible minimum load bearing capacity expressed by the EN line categories [EN 15528]. Whereas in the past, in passenger traffic, heavy locomotives or power cars were used with light wagons (e.g. 16 t), wheelset loads of up to 22 t are achieved over the entire train length. In consequence, the known dynamic coefficients lose their validity. In addition, train sets are becoming more efficient, so that regional multiple units are now expected to operate at speeds of up to 200 km/h and locomotive hauled passenger vehicles at speeds of up to 230 km/h. Due to cost pressure for railway manufacturers, different customised vehicle concepts with different excitation patterns (locomotive + wagon pushed, multiple units with/without power car, different wheelset load patterns AB, CB, SA, excitation of different wavelengths) are developed. An adaptation of infrastructure to the new rolling stock is possible for new bridges (built for other reasons than dynamics), however, the renewal of existing bridge structures is very costly (disruption of traffic, planning and construction costs). The IM has, therefore, always strived to maintain the infrastructure as long as possible. When introducing new trains such as ICE4 or ECx, verifications are necessary at a large number of bridges of the overall network or at least the operational network. As simple estimates are becoming increasingly difficult in this context, the IM calculates individual existing structures dynamically (step by step concept DB Netz in [TNB, Grunert 2022]). It becomes apparent that the hidden reserves of the infrastructure (difference between model and reality) must be proven through measurements in order to update the models and prolong the lifetime of certain structures. There are also bridges in the inventory which, for historical reasons or due to ageing, have less load bearing capacity than required for LM71. The heterogeneous DB bridge stock with its characteristics is challenging, especially if verifications are only scarce. For this purpose, databases are used to hold the structure’s data, to supplement it with load data (e.g. passing vehicles’ timetable), to complement the data with calculation results and to assign it to an assessment. In addition, a post processing presentation method of the results was also developed in order to derive simplified verifications of existing or new structures. The contribution will consist of the following parts: 1) short overview of existing bridge stock 2) introduction of the used data landscape 3) presentation of the static and dynamic effects in v/n diagrams, derivation of monitoring installations 4) application of Machine Learning to the 1st bending natural frequency 5) recent developments of digital twins in the DB environment (overview of research projects) 6) development of model and result interfaces

The dynamic response of high-speed railway bridges is a key performance parameter, both for designing new bridges (1, 2) and for evaluating existing bridges (3). In order to establish long-term continuous monitoring based on vibration measures, it is required to develop an efficient and realistic numerical model -or digital twin- with which to compare dynamic measurements. Long viaducts with continuous decks are efficient and often used solutions for new high-speed lines, exhibiting a marked redundant structural behaviour. Regarding their dynamic response, a key feature is that several vibration modes significantly influence the transient response for any single point in the viaduct. This influence differs from simpler structures that exhibit a fundamental mode for the dynamic response. In this work, La Marota viaduct is studied to demonstrate the feasibility of using suitable structural beam-type finite element (FE) models. This structure is located in Cordoba (Spain) and belongs to the Spanish high-speed railway. It has a 381 m length distributed in nine reinforced concrete spans. First, a detailed 3D continuum FE model was built and calibrated based on the performed operational modal analyses, here twenty vibration modes were experimentally obtained and the first ten used for calibration. The good agreement between the experimental and numerical results in frequency and modal shape guaranteed the procedure. Then, a novel beam-type FE model was built and calibrated to have the same dynamic response as the 3D FEM, considering also the first ten vibration modes. The advantage of this beam-type model was its low number of elements and low computational time cost concerning the 3D model. Finally, transient dynamic analyses were performed in the simplified beam-type model under the action of different high-speed trains. The results were compared with acceleration data recorded at each span during the experimental tests. The comparison in terms of the peak acceleration, root-mean-square (RMS) and moving RMS of accelerations between the real and numerical results confirmed the accuracy of the structural beam-type model that could also be used for further predictions. References 1 EN 1991-2:2003. 2003. Eurocode 1: Actions on structures – Part 2: Traffic loads on bridges. European Committee for Standardization. 2 EN 1990:2002+A1. 2005. Eurocode – Basic of structural design. European Committee for Standardization. 3 TSI Infraestructure: Technical Specifications for Interoperability. 2016. European Parliament and Council. Directive (EU) 2016/797.