Influence of rate-independent hysteresis on the dynamic response of a railway bridge

It is well known that the dynamic properties of civil engineering structures have a more or less pronounced amplitude dependency. However, it is rather difficult to quantify this both experimentally and theoretically. This paper describes an attempt to identify the sources of the amplitude dependent variation of the natural frequency and the modal damping ratio of the first vertical bending mode of a simply supported, ballasted steel-concrete composite railway bridge. It is proposed that the most likely sources to the non-linear properties of this mode of vibration are the ballasted track, the foundations and the roller bearings used mainly to relive constraint forces due to changes in temperature. The non-linear influence of the suggested sources were modelled in a 2D finite element model using the classical univariate Bouc-Wen model which was implemented as a user-defined element in ABAQUS. The results suggest that the roller bearings alone can give account for the variation in the dynamic properties observed in experimental data from the bridge and that the combination with a simple model of the track superstructure gives the most realistic result. A tremendous increase in the dissipation of energy was found as the amplitude of vibration was increased beyond that available in the experimental data, thus motivating further research within this field.