The parametric instability of a moving mass / oscillator has been studied in literature for a continuous periodic inhomogeneous Euler-Bernoulli beam, a periodic discretely supported string, and a periodic discretely supported Timoshenko beam. It was found that the parametric instability was caused by the radiation of Anomalous Doppler waves and small parametric studies to the influence of various parameters were done. In this present study, we used a periodic discretely supported Euler-Bernoulli beam and a more extensive study on the effects of various parameters was performed. For example, it was shown that in the case of an Euler-Bernoulli beam we have no destabilisation by viscosity, the instability zones merely become smaller. Results also point towards a possible relation between the dispersion characteristics of the periodic structure and the instability zones: the former dictates the possible travelling waves through the infinite kinematic invariants, which may be either anomalous or normal Doppler, that contribute to the (de)stabilisation of the moving mass / oscillator. Furthermore, the rail-sleeper system was coupled with a 2D discrete lattice that models either ballast or a slabbed track and the underlying soil foundation. By which we found that for a moving train on ballasted track parametric instability will be very unlikely: the radiation damping simply prohibits the mass becoming unstable. On the contrary, a high speed train on a slabbed track could still be unstable. This analysis also showed that the coupling of the supports through the medium likely has an effect on the instability domains.

As a short bridge is subject to a high speed train traveling over it with (sub-)resonance speeds, the dynamic interactions between the supporting bridge and moving train plays an important role in estimating the resonance speeds of the bridge for its coupling effects may result in the bridge response reducing and further down-shift the (sub-)resonant speeds. However, the well-developed theoretical (sub-)resonant speed (= fD/n) with n=1,2,3… of a typical railway bridge is only related to the bridge frequency (f) and car length (D), but the train-bridge-interaction (TBI) effects were neglected. Such an overestimatio of resonance speeds may result in mistaking the train-induced reonance of the bridge in design stage. To predict the sub-resonance speed(s) of a short railway bridge that can take TBI effects into account, an equivalent modal mass method will be proposed so that the down-shifted frequency due to the presence of multiple train cars on the bridge can be accounted for. From numerical demonstrates, the proposed method can estimate the shifted resonant speeds and further explain the shifted-resonance phenomenon of short railway bridges under train passage.

Railway tracks experience differential settlement due to the stresses induced during train-track interaction. The characteristics of this vertical profile are a key parameter when scheduling track maintenance operations. Regression or machine learning can be used to extrapolate historical changes in profile, however this approach is challenging when linespeed is increased or new rolling-stock is introduced. As a solution, this paper presents a novel approach to investigate the effect of increasing train speeds, adding additional passenger movements and adding additional freight movements to an existing line. The model combines empirical settlement laws with 2.5D finite element theory, where the track-ground structure is modelled explicitly, and multi-body train-track interaction is considered. The stresses are computed using a hybrid frequency-wavenumber and time-space approach, considering non-linear track-soil material behaviour. It is shown that higher speeds result in elevated dynamic forces and cause a faster rate of deterioration of track geometry. The model also investigates the effect of adding additional train movements to a passenger line. It is shown that additional movements increase the rate of track degradation, particularly if the additional traffic is freight. This is because freight vehicles typically have one only layer of suspension, thus generating elevated dynamic forces compared to passenger vehicles.

The main purpose of the present study is to investigate the effects of damage phenomena on the structural behaviour of Reinforced Concrete (RC) bridges and related identification procedure. To this end, an effective FE numerical model able to analyse the structural response, in presence of different damage scenarios, is implemented. Moreover, the influence of moving loads on the damage behaviour is also considered by means of vehicle-bridge interaction (VBI) FE model. The combination of the structural model and the vehicle mechanical system provides an advanced numerical model able to simulate the dynamic interaction between bridge and moving vehicle. This problem is managed by using moving mesh technique. In particular, the formulation “Arbitrary Lagrangian-Eulerian’’ (ALE) provides an accurate description of the interaction between two systems. ALE approach is based on a fixed-referential system and moving coordinate variables, representing the positions of the computational nodes during the application of the moving loads. Vibrational analyses in terms of damage scenarios are presented to verify how the presence of material discontinuities affect the natural frequencies of the structural system. Moreover, results in terms of dynamic amplification factor for typical design bridge variables, in presence of damage phenomena and moving loads, are also developed. Finally, a discussion on the impact of the proposed results on the dynamic identification procedures is provided.