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Vibration of the railway track-viaduct system under moving vehicles taking into account the interaction effect

Railway track irregularities consist of a deviation of the inside edge of the rail from the ideal geometric rail contour and may occur even during the passage of the vehicle at a very low speed. Track irregularities can influence the dynamic behaviour of railways bridges and increase dynamic load effects. This paper addresses the influence of different irregularities on the dynamic behaviour of a medium span bridge. Random irregularities, continuous all over the rail, are considered. The maximum response of the bridge, displacements and accelerations, at the mid span is calculated. For these calculations the dynamic model of the ballast track, present in the ERRI studies, is used and the response of the ballast is also analysed.

The main purpose of this paper is to present some results concerning the investigation that has been done by the authors regarding the dynamic response of small to médium span railway bridges using response acceleration data colleted during the measurements carried out on single span bridges on the railway track Linz-Wels, in Austria. Using output-only methods in this experimental program, it was possible to have an estimation of the igenfrequencies, mode shapes and the corresponding viscous damping. Due to the fact that the bridges were of the same type some generalizations concerning their structural behavior was possible and finite element models were calibrated in order to compute responses for real traffic. The numerical model of the bridges takes into account the track and the real boundary conditions of the decks. The measured and the computed acceleration responses of the track/bridge system are compared using two methods: the moving forces method and the interaction vehicle/track/bridge method.

As irregularidades na via-férrea influenciam o comportamento dinâmico das pontes ferroviárias e aumentam os efeitos dinâmicos produzidos pela passagem dos eixos do comboio. Neste estudo é analisada a influência das irregularidades da via-férrea na resposta dinâmica de uma ponte, cuja primeira frequência natural de vibração se encontra sobre os limites definidos no Eurocódigo 1. São consideradas diferentes irregularidades, isolada a meio-vão e contínua de amplitude aleatória existente em toda a extensão do carril. As respostas máximas da ponte com as irregularidades são determinadas em termos de deslocamentos e acelerações, e comparadas com as obtidas sem as irregularidades. Recorre-se ao modelo dinâmico de via-férrea balastrada ERRI. São analisadas as acelerações na massa vibrante do balastro via-férrea bem como as forças de contacto entre a roda e o carril.

Due to the need for increasing train speeds several existing small to medium span bridges in the track Linz-Wels (Austria) were re-evaluated. In a preliminary numerical calculation, considering conservative values for the dynamic parameters, very high vertical accelerations were computed for some of those structures. An experimental program was thus carried out in order to get a better estimation for the dynamic behaviour of the bridges, concerning mainly the first vertical eigenfrequency and the corresponding viscous damping. The paper reports on the results of this experimental investigation and identifies some areas where further research is necessary.