Paulius Bucinskas

Efficiency of Nearly Periodic Structures for Mitigation of Ground Vibration

Periodic structures are known to produce passbands and stopbands for propagation of vibration energy within the frequency domain. Sources vibrating harmonically at a frequency within a passband can lead to propagation of energy through propagating modes over long distances. However, sources vibrating at a frequency within a stopband excite only nearfields in the form of attenuating and evanescent modes, and the energy decays with distance. The decay phenomena are due to destructive interference of waves reflected and scattered by interfaces or obstacles placed periodically within or between the repeated cells of the structure. For a truly periodic structure, the vibration level within a stopband goes toward zero after infinitely many repetitions of the cell. For example, employing a two-dimensional model, Andersen [1] found that stopbands for ground vibration in the low-frequency range can be introduced by periodic inclusions or changes to the ground surface geometry. However, for vibration mitigation in the context of real civil-engineering problems related to ground-borne noise from railways, for example, the excitation is not strictly harmonic and a steady state of the response is usually not achieved. Further, only a limited number of repetitions of wave impedance blocks or barriers can be made in practice, and in three dimensions, the inclusions have finite extent in the direction orthogonal to the array. Similarly to the work by Andersen et al. [2], this paper addresses the question whether repeated structures of nearly periodic nature can be used to mitigate vibrations caused by non-stationary sources. For this purpose, wave impedance blocks with finite numbers of repetitions are compared to their truly periodic counterparts. Firstly, a two-dimensional study is conducted with focus on studying the nature of wave modes in a periodic array of wave impeding blocks. Secondly, three-dimensional analysis is performed in the frequency domain, focusing on the insertion loss provided by increasing numbers of repetitions of blocks with different height and embedment. Finally, the insertion loss provided by nearly periodic structures is examined, and the mitigation efficiency of wave-impeding-block arrays is quantified in the case of transient loads. Lars V. Andersen, Andrew Peplow and Paulius Bucinskas

Excitation of Structures Near Railway Tracks-Analysis of the Wave Propagation Path

High-speed rails are an attractive alternative to other forms of intercity transportation. It is a fast, cost-efficient and environmentally friendly solution, which is being developed in various countries across the world. However, in order to be successful, high-speed rails need to transport the passengers as close as possible to the city centres. Therefore, railway tracks have to go through densely populated urban areas, which causes a number of issues. One of the biggest complaints from the inhabitants living near such infrastructures is the high vibration and noise levels caused by the passing trains. Unfortunately, the prediction of vibrations in nearby structures is difficult, as wave propagation from the vibration source to the structure is a complex phenomenon. The behaviour of the structure is highly dependent on the path along which the vibrations travel between their source and the building itself. Especially in the densely built urban environment, the wave propagation path can have different features, such as underground infrastructure, roads, pavements or even other nearby buildings. Such features might have a significant effect on the final excitation of the structure in question. This work aims to analyse how different features in the wave propagation path affect the excitation of a structure. A numerical model is constructed to account for the track structure and the underlying soil. The model utilizes a finite-element model for the structures together with a semi-analytical model of the underlying soil. Different features in the wave-propagation path are introduced, and their effects are compared regarding the behaviour of the structure and the free-field. Paulius Bucinskas and Lars V. Andersen