Keywords: railway bridge dynamics, multiple units, dynamic response, resonance, impact, reference load model, finite element models, train characteristics, compatibility checks.

Civil engineers are nowadays aware of the dynamic problems that can occur on railway bridges, including impact and resonance effects. These considerations are detailed for new bridges in the EN1991-2. However, characterising the load capacity of existing bridges on a line for these dynamic effects arising from different rolling stock is not an easy task. The characterisation of an entire line requires very extensive calculations and experience in these types of studies.

Moreover, it has been noticed in several European countries that recent multiple units (whether with a shorter coach length or with a higher axle load) have the potential to create dynamic problems at around 160km/hr and above on some bridges on networks.

Therefore, this study aims to classify the dynamic load effect characteristics of multiple units (including recent developments in rolling stock design) on typical bridges of the European network, and advise rolling stock manufacturers on the types of train that could be dynamically aggressive for the infrastructure.

A series of calculations were made using finite element models of different bridges representing a wide range of typical structures in Europe: filler beams, lateral girders, twin girders, frames, etc.

In order to reduce the number of required calculations, the trains were grouped into families of similar dynamic excitation, with each family represented by a reference load model (RLM). Twelve RLMs have been created to cover most of European higher and high speed passenger rolling stock. These load models characterise the dynamic excitation of the trains where the excitation frequency of the train interacts with the vibration characteristics of the structure to produce resonance. Additional studies were carried out to investigate the effect of impacts due to the heaviest axles in a train formation, typically due to power cars or locomotives. It has been found that the presence of a locomotive with higher axle loads does not increase the dynamic effects at resonance if the loading effects from pattern of axles is not synchronised with the remainder of the train, a typical situation where the length of the locomotive is different to that of the coaches in the train. The total effect of both resonance and impact phenomena can then be obtained by taking the envelope of the results obtained at resonance and for impact effects.

The calculations show that some new passenger multiple units are more aggressive for resonance than common existing trains. On the specific examples calculated, some of the bridges are also more sensitive to resonance than others. A parametric study is recommended to assist in characterising the types of bridges most likely to experience dynamic problems. When carrying out such parametric studies or other studies to check the compatibility with existing lines of the proposed operation and speed of multiple units, the use of reference load models is recommended. The use of reference load models reduces the number of loading patterns to be checked (in comparison with the number of options permitted by the Rolling Stock Technical Specification for Interoperability) and provides useful information on the train parameters covered for future compatibility checks.

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