203 research outputs found

    Shakedown for slab track substructures with stiffness variation

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    In this paper, shakedown analyses are carried out to predict the long-term response of slab track substructures under repeated moving train loads. The train loads are converted into a distributed moving load on the substructure surface by using a simplified track analysis. Based on Melan’s static shakedown theorem, a well-established shakedown analysis method is extended to determine shakedown limits of the slab track substructures. The influence of a linearly increasing stiffness modulus on the shakedown limits is considered by conducting finite- element analysis with a user-defined material. It is found that a rise in stiffness modulus or stiffness variation ratio can either increase or decrease the shakedown limit, depending on the competitive effects of the two mechanisms. Furthermore, the subgrade thickness determines the dominant mechanism

    Analysis of the influence of under sleeper pads on the railway vehicle/track dynamic interaction in transition zones

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    [EN] Sharp changes in the vertical stiffness levels of a track can increase train and infrastructure deterioration to the point where there is a serious risk of a derailment. Major overloading and unloading forces are created between the different track and vehicle components. This phenomenon has grown in importance as the operational speeds of trains have increased with the expansion of high-speed lines. In order to solve this problem a method has to be found to smooth the changes in vertical stiffness levels along the track. In the present paper, the combination of transition regions and under- sleeper pads (USPs) has been studied. The research has been performed by means of a dynamic vehicle-track interaction model created by synthesizing a series of sub-models of individual effects. The analysed variables allow various track configurations, train travelling speeds and the stiffness of the USPs to be investigated. The obtained results show that combining transition zones with USPs pads allows more homogeneous vertical stiffness levels to be achieved along the tracks which results in improved dynamic behaviour of the vehicle-track system. © IMechE 2011.This work was supported by Ineco-Tifsa.Insa Franco, R.; Salvador Zuriaga, P.; Inarejos Mesa, J.; Roda Buch, A. (2012). Analysis of the influence of under sleeper pads on the railway vehicle/track dynamic interaction in transition zones. Proceedings of the Institution of Mechanical Engineers Part F Journal of Rail and Rapid Transit. 226(4):409-420. doi:10.1177/0954409711430174S409420226

    Effectiveness of resilient wheels in reducing noise and vibrations

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    This study focuses on the effectiveness of resilient wheels in reducing railway noise and vibrations, and compares the effectiveness of three types of wheels. The finite elements method has been used to characterise the vibratory behaviour of these wheels. The model has been excited with a realistic spectrum of vertical track irregularities, and a spectral analysis has been carried out. Results have been post-processed in order to estimate the sound power emitted. These calculations have been used to assess the effectiveness of the resilient wheel designs in reducing noise emitted to the environment and in propagating structural vibrations

    Analytical model for predicting the buckling load of continuous welded rail tracks

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    The use of continuous welded rail (CWR) track has solved many of the problems associated with tread surface discontinuities that occur in jointed tracks. However, due to the longitudinal expansion of the rails in CWR tracks being highly constrained, the generated compressive stresses in the rails can cause track buckling in the horizontal plane. Track buckling is a complex phenomenon, in which many factors are involved and around which there is much uncertainty. The objective of this paper is to present an analytical model that can be used to calculate the buckling load of a CWR track. This model accounts for the contributions of base, crib and shoulder ballast and includes the effect of vertical loading on each of these components. Moreover, a parametric study based on this model is developed, in order to understand how and the extent to which the considered factors affect track stability. The results of the study indicate that the characteristics of the existing misalignments in the track are the critical parameters involved in the phenomenon. In addition, maintenance operations that affect the ballast, such as tamping or surfacing, and the dimensions and material of the track sleepers are also important factors.Navarro Martinez, JI.; Villalba Sanchis, I.; Martínez Fernández, P.; Insa Franco, R. (2015). Analytical model for predicting the buckling load of continuous welded rail tracks. Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit. 229(5):542-552. doi:10.1177/0954409713518039S5425522295Kerr, A. D. (1978). Analysis of thermal track buckling in the lateral plane. Acta Mechanica, 30(1-2), 17-50. doi:10.1007/bf01177436Grissom, G. T., & Kerr, A. D. (2006). Analysis of lateral track buckling using new frame-type equations. International Journal of Mechanical Sciences, 48(1), 21-32. doi:10.1016/j.ijmecsci.2005.09.006Le Pen, L. M., & Powrie, W. (2011). Contribution of Base, Crib, and Shoulder Ballast to the Lateral Sliding Resistance of Railway Track: A Geotechnical Perspective. Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit, 225(2), 113-128. doi:10.1177/095440971039709

    A study on wear evaluation of railway wheels based on multibody dynamics and wear computation

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    The wear evolution of railway wheels is a very important issue in railway engineering. In the past, the reprofiling intervals of railway vehicle steel wheels have been scheduled according to designers' experience. Today, more reliable and accurate tools in predicting wheel wear evolution and wheelset lifetime can be used in order to achieve economical and safety benefits. In this work, a computational tool that is able to predict the evolution of the wheel profiles for a given railway system, as a function of the distance run, is presented. The strategy adopted consists of using a commercial multibody software to study the railway dynamic problem and a purpose-built code for managing its pre- and post-processing data in order to compute the wear. The tool is applied here to realistic operation scenarios in order to assess the effect of some service conditions on the wheel wear progression

    Analysis of the performance of under-sleeper pads in highspeed line transition zones

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    [EN] In many high-speed railway lines, the zones between embankments and structures may present some discontinuities, in terms of track geometry and track stiffness, which may create discomfort for passengers, induce deterioration of track and vehicle materials and even raise the risk of derailment to dangerous levels. In the attempt to attenuate the consequences of such problems, some solutions pointing at progressively changing the vertical stiffness in the railway track have been tested, such as transition zones or pads placed either between the rails and the sleepers or under the sleepers. The contribution of under-sleeper pads in transition regions and their effect on the railway infrastructure is specifically analysed in the present paper. The results obtained are of interest since they provide useful information for railway managers on infrastructure design and justify the need to implement such transition ones.Insa Franco, R.; Salvador Zuriaga, P.; Inarejos Mesa, J.; Medina González, L. (2014). Analysis of the performance of under-sleeper pads in highspeed line transition zones. Proceedings of the Institution of Civil Engineers - Transport. 167(2):63-77. doi:10.1680/tran.11.00033S6377167

    Plausible Petri nets as self-adaptive expert systems: A tool for infrastructure asset monitoring

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    This article provides a computational framework to model self-adaptive expert systems using the Petri net (PN) formalism. Self-adaptive expert systems are understood here as expert systems with the ability to autonomously learn from external inputs, like monitoring data. To this end, the Bayesian learning principles are investigated and also combined with the Plausible PNs (PPNs) methodology. PPNs are a variant within the PN paradigm, which are efficient to jointly consider the dynamics of discrete events, like maintenance actions, together with multiple sources of uncertain information about a state variable. The manuscript shows the mathematical conditions and computational procedure where the Bayesian updating becomes a particular case of a more general basic operation within the PPN execution semantics, which enables the uncertain knowledge being updated from monitoring data. The approach is general, but here it is demonstrated in a novel computational model acting as expert system for railway track inspection management taken as a case study using published data from a laboratory simulation of train loading on ballast. The results reveal selfadaptability and uncertainty management as key enabling aspects to optimize inspection actions in railway track, only being adaptively and autonomously triggered based on the actual learnt state of track and other contextual issues, like resource availability, as opposed to scheduled periodic maintenance activities.Lloyd'sRegister Foundation, Grant/Award Number: RB4539; Engineering and Physical SciencesResearch Council, Grant/Award Number:EP/M023028/

    On the ballast–sleeper interaction in the longitudinal and lateral directions

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    In service, railway tracks must withstand transverse and longitudinal forces arising from running vehicles and thermal loads. The mechanical design adopting any of the track models available in the technical literature requires that the strength of the track is fully characterized. In this paper, the results of an experimental research activity on the sleeper-ballast resistance along the lateral and the longitudinal directions are reported and discussed. In particular, the work is aimed at identifying the strength contributions offered by the base, the ballast between the sleepers, and the ballast shoulder to the global resistance of the track in the horizontal plane. These latter quantities were experimentally determined by means of an ad hoc system designed by the authors. Field tests were carried out on a series of track sections that were built to simulate scenarios in which the ballast was removed from the crib and/or the shoulder. The results of this study indicate that, as far as the scenarios here investigated are concerned, the strength percent contributions from the crib, the sleeper base and the shoulder are respectively equal to about 50%, 25%, and 25% in the lateral direction, and 60%, 30%, and 10% in the longitudinal one. Moreover, the comparison of the acquired data with literature results reveals that a detailed knowledge both of the testing conditions and the activated ballast failure mechanisms are needed in order to correctly use test data for design purpose

    A Novel Bacteriophage with Broad Host Range against Clostridioides difficile Ribotype 078 Supports SlpA as the Likely Phage Receptor

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    Bacteriophages represent a promising option for the treatment of Clostridioides difficile (formerly Clostridium difficile) infection (CDI), which at present relies on conventional antibiotic therapy. The specificity of bacteriophages should prevent dysbiosis of the colonic microbiota associated with antibiotic treatment of CDI. While numerous phages have been isolated, none have been characterized with broad host range activity toward PCR ribotype (RT) 078 strains, despite their relevance to medicine and agriculture. In this study, we isolated four novel C. difficile myoviruses: ?CD08011, ?CD418, ?CD1801, and ?CD2301. Their characterization revealed that each was comparable with other C. difficile phages described in the literature, with the exception of ?CD1801, which exhibited broad host range activity toward RT 078, infecting 15/16 (93.8%) of the isolates tested. In order for wild-type phages to be exploited in the effective treatment of CDI, an optimal phage cocktail must be assembled that provides broad coverage against all C. difficile RTs. We conducted experiments to support previous findings suggesting that SlpA, a constituent of the C. difficile surface layer (S-layer) is the likely phage receptor. Through interpretation of phage-binding assays, our data suggested that ?CD1801 could bind to an RT 012 strain only in the presence of a plasmid-borne S-layer cassette corresponding to the slpA allele found in RT 078. Armed with this information, efforts should be directed toward the isolation of phages with broad host range activity toward defined S-layer cassette types, which could form the basis of an effective phage cocktail for the treatment of CDI

    Discrete element modelling of scaled railway ballast under triaxial conditions

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    The aim of this study is to demonstrate the use of tetrahedral clumps to model scaled railway ballast using the discrete element method (DEM). In experimental triaxial tests, the peak friction angles for scaled ballast are less sensitive to the confining pressure when compared to full-sized ballast. This is presumed to be due to the size effect on particle strength, whereby smaller particles are statistically stronger and exhibit less abrasion. To investigate this in DEM, the ballast is modelled using clumps with breakable asperities to produce the correct volumetric deformation. The effects of the quantity and properties of these asperities are investigated, and it is shown that the strength affects the macroscopic shear strength at both high and low confining pressures, while the effects of the number of asperities diminishes with increasing confining pressure due to asperity breakage. It is also shown that changing the number of asperities only affects the peak friction angle but not the ultimate friction angle by comparing the angles of repose of samples with different numbers of asperities
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