Airborne and Ground-Borne Noise and Vibration from Urban Rail Transit Systems

The environmental effect of ground-borne vibration and noise generated by urban rail transit systems is a growing concern in urban areas. This chapter reviews, synthesizes and benchmarks new understandings related to railway vibration and associated airborne and ground-borne noise. The aim is to provide new thinking on how to predict noise and vibration levels from numerical modelling and from readily available conventional site investigation data. Recent results from some European metropoles (Brussels, Athens, etc.) are used to illustrate the dynamic effect of urban railway vehicles. It is also proved that train type and the contact conditions at the wheel/rail interface can be influential in the generation of vibration. The use of noise-mapping-based results offers an efficient and rapid way to evaluate mitigation measures in a large scale regarding the noise exposure generated to dense urban railway traffic. It is hoped that this information may provide assistance to future researchers attempting to simulate railway vehicle vibration and noise

The effect of railway local irregularities on ground vibration

The environmental effects of ground-borne vibrations generated due to localised railway defects is a growing concern in urban areas. Frequency domain modelling approaches are well suited for predicting vibration levels on standard railway lines due to track periodicity. However, when considering individual, non-periodic, localised defects (e.g. a rail joint), frequency domain modelling becomes challenging. Therefore in this study, a previously validated, time domain, three-dimensional ground vibration prediction model is modified to analyse such defects. A range of different local (discontinuous) rail and wheel irregularity are mathematically modelled, including: rail joints, switches, crossings and wheel flats. Each is investigated using a sensitivity analysis, where defect size and vehicle speed is varied. To quantify the effect on railroad ground-borne vibration levels, a variety of exposure–response relationships are analysed, including: peak particle velocity, maximum weighted time-averaged velocity and weighted decibel velocity. It is shown that local irregularities cause a significant increase in vibration in comparison to a smooth track, and that the vibrations can propagate to greater distances from the line. Furthermore, the results show that step-down joints generate the highest levels of vibration, whereas wheel flats generate much lower levels. It is also found that defect size influences vibration levels, and larger defects cause greater vibration. Lastly, it is shown that for different defect types, train speed effects are complex, and may cause either an increase or decrease in vibration levels

Modelling the Environmental Effects of Railway Vibrations from Different Types of Rolling Stock: A Numerical Study

This paper analyses the influence of rolling stock dynamics on ground-borne vibration levels. Four vehicle types (Thalys, German ICE, Eurostar, and Belgian freight trains) are investigated using a multibody approach. First, a numerical model is constructed using a flexible track on which the vehicles traverse at constant speed. A two-step approach is used to simulate ground wave propagation which is analysed at various distances from the track. This approach offers a new insight because the train and track are fully coupled. Therefore rail unevenness or other irregularity on the rail/wheel surface can be accurately modelled. Vehicle speed is analysed and the frequency spectrums of track and soil responses are also assessed to investigate different excitation mechanisms, such as carriage periodicities. To efficiently quantify train effects, a new (normalised) metric, defined as the ratio between the peak particle velocity and the nominal axle load, is introduced for a comparison of dynamic excitation. It is concluded that rolling stock dynamics have a significant influence on the free field vibrations at low frequencies, whereas high frequencies are dominated by the presence of track unevenness

Proposal of a CLT reinforcement of old timber floors

Despite the fact that, from the mechanical point of view, there is no ageing issues of timber elements when they are properly used, many old timber structures require important interventions because of changes in uses (which modifies the regulating rules for example), of material decay (misuse of timber) or possibly of a faulty design or construction. In particular, timber floors in old structures often present large deflections and most the time had been designed for a maximum load much lower than the one prescribed by contemporary rules. After an introduction about timber floors and a short review about the reinforcement technics that exist, the present paper presents a new proposal for their reinforcement. The solution developed in the present paper uses a Cross Laminated Timber (CLT) panel screwed over the existing floor, keeping a small gap between the panel and the existing joists. In this way, the new “composite” floor presents higher stiffness and the gap is used for horizontal line runs. For the design of such a “composite floor”, modified Johanssen’s equations (including the gap between the CLT panel and the joists) are proposed and their application on a case study is presented.- (undefined

MBS/FEM co-simulation for hybrid modeling of railway dynamics

Nowadays in railway traffic, specific speed limitations exist depending on the train charge, due to a fragile subsoil or even an old building that has to be preserved. Depending on the type of vehicle, the type of soil or even the vehicle speed, the groundborne vibration characteristics can significantly vary. It becomes thus important to predict the vibrations generated by a train passing on a track in the surrounding soil. In order to achieve this prediction, a hybrid modeling approach, consisting in a vehicle modeled using the minimal coordinates approach in multibody systems theory and a soil modeled using a finite element method, is developed. The recoupling of this hybrid system is performed using co-simulation between two different software packages with their own solvers. The first software is EasyDyn, an in-house C++ library package dedicated to multibody dynamics and the second software is ABAQUS that is dedicated to finite element analysis. The aim of this paper is to illustrate the results given by this hybrid model. Then two different co-simulation schemes (the sequential Gauß-Seidel scheme and the parallel Jacobi scheme) will be used and compared in terms of accuracy for this specific railway application

A 2.5D time-frequency domain model for railway induced soil-building vibration due to railway defects

A new hybrid time-frequency modelling methodology is proposed to simulate the generation of railway vibration caused by singular defects (e.g. joints, switches, crossings), and its propagation through the track, soil and into nearby buildings. To create the full source-to-received model, first the force density due to wheel-rail-defect interaction is calculated using a time domain finite element vehicle-track-soil model. Next, the frequency domain track-soil transfer function is calculated using a 2.5D boundary/finite element approach and coupled with the force densities to recover the free-field response. Finally, the soil-structure interaction of buildings close to the line is computed using a time domain approach. The effect of defect type, train speed and building type (4-storey office block and 8-storey apartment building) on a variety of commonly used international vibration metrics (one-third octaves, PPV, MTVV) is then investigated. It is found that train speed doesn't correlate with building vibration and different defect types have a complex relationship with vibration levels both in the ground and buildings. The 8-storey apartment building has a frequency response dominated by a narrow frequency range, whereas the modal contribution of the 4-storey office building is over a wider frequency band. This results in the 8-storey building having a higher response

Assessment of railway ground vibration in urban area using in-situ transfer mobilities and simulated vehicle-track interaction

This article proposes an alternative approach to the well-known Federal Railroad Administration method to evaluate ground vibrations induced by the passing of railway vehicles. The originality lies on the excitation mechanisms that occur in urban areas. A common source of railway-induced ground vibrations is local defects (rail joints, switches, and turnouts) which cause large amplitude excitations at isolated locations along the track. To analyse such situations, a combined numerical-experimental study is developed, based on the use of numerical train/track results and experimental mobility transfer functions. The influence of building foundation type, vehicle, defect type, and size and location is evaluated through experimental data collected in Brussels (Belgium). The results show that it is possible to assess vibrations from light rapid transit systems in the presence of local rail defects and unknown soil conditions