The Effect of Soil Non-linearity on Mixed Traffic Railway Lines: Passenger vs Freight Loads

To add additional capacity to railway networks, freight services might be added to lines that have previously only be used for passenger services. Existing ballasted lines may have mixed subgrade conditions and thus the effect of increased axle loads on track behavior is unclear. Typically, such cases will result in elevated track deflections in comparison to passenger vehicles. As a result, the supporting subgrade experiences higher strain levels, which can fall into the large strain range. The related non-linear subgrade behavior plays an important role in track response but is challenging to model. As a solution, this paper presents a new semi-analytical numerical model, where the track is simulated analytically and allows for 1D wave propagation. The ground is modelled using a non-linear equivalent thin-layer finite element formulation. This allows for the subgrade stiffness to be updated in an iterative manner with minimal computational effort. A case study is presented to show that modest increases in axle load can have a marked effect on track deflections

Railway-induced ground vibrations – a review of vehicle effects

This paper is a review of the effect of vehicle characteristics on ground- and track borne-vibrations from railways. It combines traditional theory with modern thinking and uses a range of numerical analysis and experimental results to provide a broad analysis of the subject area. First, the effect of different train types on vibration propagation is investigated. Then, despite not being the focus of this work, numerical approaches to vibration propagation modelling within the track and soil are briefly touched upon. Next an in-depth discussion is presented related to the evolution of numerical models, with analysis of the suitability of various modelling approaches for analysing vehicle effects. The differences between quasi-static and dynamic characteristics are also discussed with insights into defects such as wheel/rail irregularities. Additionally, as an appendix, a modest database of train types are presented along with detailed information related to their physical attributes. It is hoped that this information may provide assistance to future researchers attempting to simulate railway vehicle vibrations. It is concluded that train type and the contact conditions at the wheel/rail interface can be influential in the generation of vibration. Therefore, where possible, when using numerical approach, the vehicle should be modelled in detail. Additionally, it was found that there are a wide variety of modelling approaches capable of simulating train types effects. If non-linear behaviour needs to be included in the model, then time domain simulations are preferable, however if the system can be assumed linear then frequency domain simulations are suitable due to their reduced computational demand

Effect of kinematic interaction on seismic response of offshore wind turbines on monopiles

Interest in renewable energy over the past decade has motivated a remarkable research on offshore wind energy. Due to the environmental loading conditions in the early developments of offshore wind farms, the focus of the research and engineering has been on aerodynamic and hydrodynamic subjects. However, earthquake has turned out to be a major design concern in seismic areas such as East Asia, Southern Europe, and United States. The topics include, among others, nonlinear response of foundations, soil liquefaction, and their impacts on foundation performance. An important topic in seismic soil‐structure interaction (SSI) analysis is the kinematic seismic response of foundations. This information is crucial for analyses based on the substructuring approach where both kinematic response and foundation impedances are key parameters. While considerable research has been spent on the latter topic, very little has been reported on the kinematic interaction. Large monopoles with low aspect ratios tend to rotate much more than regular piles in pile group foundations due to seismic waves. The rotation leads to additional load on the tower and the turbine. This article uses a rigorous numerical model for monopole‐soil interaction in layered soil and computes both rotational and horizontal responses at the pile head (seabed) as functions of frequency. A suite of generic homogeneous and heterogeneous soil profiles with shear moduli representative of clay (generally linear) and sand (generally parabolic) are considered in these analyses. Through representative analyses, both in frequency domain and time domain, it is illustrated how the kinematic interaction influences the earthquake loads imparted to an offshore wind turbine (OWT)