on the lateral stability of the sleeper ballast system

Abstract The lateral stability of railway tracks depends on all track components: rails, fastening systems, sleepers, ballast bed and substructure. Among them, the ballast is the weakest one and, due to its granular nature, experimental data obtained in line from full-scale tests, rather than based on analytical formulations, are used to describe its behavior. Until now, several studies have been carried out to quantify the effects of the track-bed geometrical parameters on the transverse strength of the track, but unfortunately not all the possible scenarios have been investigated. To fill this gap, a numerical-experimental research program of in-line tests has been developed in the framework of a cooperation between the Italian State Railways (RFI) and the Department of Industrial Engineering (DII) of the University of Naples Federico II. An ad hoc experimental testing plant, which is able to apply in a more realistic way the testing loads in field conditions, has been designed and realized. In the present paper, the test field is described, and both the features of the new testing plant and the advantages that this new system offers are detailed. Finally, from the analysis of the experimental data obtained from in-line tests carried out on some track panels representative of real scenarios, and with the help of atypical lateral resistance tests, an interesting property is utilized to predict a priori the lateral resistance curves of non tested scenarios

On the homogenization of periodic beam-like structures

Abstract A homogenization method for periodic beam-like structures that is based on the unit cell force transmission modes is presented. Its main advantage is that to identify the principal vectors of the state transfer matrix corresponding to the transmission modes it operates directly on the sub-partitions of the unit cell stiffness matrix and allows to overcome the problems due to ill-conditioning of the transfer matrix. As case study, the Pratt girder is considered. Closed form solutions for the transmission modes of this girder are achieved and used into homogenization. Since the pure bending mode shows that the Pratt unit cell transmits two kinds of bending moments, one given by the axial forces and the other originated by nodal moments, the Timoshenko couple-stress beam is employed as substitute continuum. Finally, a validation of the proposed procedure is carried out comparing the predictions of the homogenized models with the results of a series of girder f.e. analyses

On the fatigue improvement of railways superstructure components due to cold expansion – Part II: Finite element prediction

This paper is the second of a two-part series dealing with the study of the residual stress field induced by cold expansion (CE) in rail-end-bolt holes. In the aeronautical field, cold expansion is a consolidated practice adopted to induce beneficial residual compressive stresses around holes of aluminium parts, with the aim to improve the fatigue strength. However, in the literature few experimental or numerical studies are proposed on the application of this technique to structural steels. In Part I, an in-depth experimental investigation was carried out on railway steel, in particular on rail-end-bolt holes, with the aim to better understand the full non-linear response of the material during the whole process. In this paper, finite element (FE) analyses simulating CE process are presented, and the experimental results of Part I have been used to validate the FE model. The strain-time history acquired during the entire cold expansion process allowed the comparison with FE-predicted strains, both in terms of residual and maximum strains. This approach is not present in literature, neither for aluminium nor for steel. The results, in terms of trend and magnitude, show that strains in both the experiments and the FE simulations are generally consistent, confirming the reliability of the FE model. In addition, a sensitivity study is presented for different levels of cold expansion. The results can be exploited to develop an a priori prediction of the residual stresses near the hole surface, aiming to an improvement of fatigue strength

Transverse strength of railway tracks : Part 2. Test system for ballast resistance in line measurement

© Gruppo Italiano Frattura 2014. This is an Open Access article distributed in accordance with the terms of the Creative Commons Attribution (CC BY 4.0) license, which permits others to distribute, remix, adapt and build upon this work, for commercial use, provided the original work is properly cited. See: https://creativecommons.org/licenses/by/4.0/In the present paper, testing methods currently adopted to measure the in service ballast resistance are synthetically reviewed to identify the main sources of uncertainty influencing the test loads and to define an experimental methodology allowing the optimal control of the testing parameters without the introduction of spurious or parasitic actions on the track sample. An alternative testing system, which allows applying on a full-scale sample of a railway track testing loads very close the real ones, is presented. Of the new system, both the ways of use for measuring the transversal and axial ballast strength, the general procedure to carry out the experimentation and its application to a real scenario are described, highlighting its main advantages in terms both of modalities for applying the loads and of testing parameter control.Peer reviewe

An inertizing and cooling process for grapes cryomaceration

Background: With this research an inertizing and cooling process for grapes cryomaceration has been set up. The process in question has been performed by an innovative plant that cooled the grapes rapidly in about 8 sec until they reached the set cryo-maceration temperature, using direct injection of liquid CO2. It works with a grape flow of approximately 2-3 tons/h, with a maximum thermal gradient of 20 K between the grape inlet and outlet temperature. For this plant a vibrating device was set up that allowed that only one grape cluster layer to be formed on the ribbon conveyor after the grapes had been put into the feedbox. A numerical model was set up for the cooling tunnel, and numerical simulations were performed to investigate the operative parameters of the machine in question. The numerical results were validated by means of experimental tests. Results: The wines obtained by using the considered plant (IW) were chemically analysed, and a comparison was performed with wines obtained with the same grape without the use of the plant (TW). All phenolic parameters were higher in IW wines, while other substances such as alcohol, reducing sugars, acids, and volatile acidity were less affected by the different winemaking technique. A deeper yellow colour was a direct consequence of the higher phenolic content of IW wines. Panelists preferred the IW wines, which had a richer, more delicate aroma. Conclusions: The study showed that careful exclusion of air combined with preventing oxidation during the cooling process, that is realized with the considered innovative cooling plant, effectively yields pleasing wines with more character

Transverse strength of railway tracks : Part 1. planning and experimental setup

© Gruppo Italiano Frattura 2014. This is an Open Access article distributed in accordance with the terms of the Creative Commons Attribution (CC BY 4.0) license, which permits others to distribute, remix, adapt and build upon this work, for commercial use, provided the original work is properly cited. See: https://creativecommons.org/licenses/by/4.0/Several studies have been carried out until now by various Research Agencies and Railway Administrations to quantify the effects of the track-bed geometrical characteristics on the transverse strength of the track. Unfortunately, not all the possible scenarios in terms of track components, track-bed cross profile, operating conditions etc. have been investigated and not all the relevant variables have been directly measured. Therefore data available from the literature have different degrees of reliability. With the aim of enlarging the knowledge on the track stability and covering much of the possible relevant scenarios, an experimental research program has been developed in the framework of a cooperation between RFI, Italcertifer and DII. In order to perform the investigation under quite general conditions and to reduce the experimentation costs, n. 28 significant scenarios have been identified and reproduced on as many independent track segments. By applying on each track segment a transversal load, the strength of the ballast-sleeper interface has been determined. The results relative to the first four scenarios are presented in terms of applied load vs. lateral track displacement diagrams and in more synthetic numerical tables.Peer reviewe

Transverse strength of railway tracks : Part 3. Multiple scenarios test field

© Gruppo Italiano Frattura 2014. This is an Open Access article distributed in accordance with the terms of the Creative Commons Attribution (CC BY 4.0) license, which permits others to distribute, remix, adapt and build upon this work, for commercial use, provided the original work is properly cited. See: https://creativecommons.org/licenses/by/4.0/In the present paper the design and construction choices of a test field for the ballast lateral resistance measurement, in order to produce data useful for the development of a numerical model able to simulate the service critical conditions of a continuous welded rail track, are described. Some construction details described herein allow to better understand the methodological approach followed in the design of experiments, the tests management philosophy as well as of the accuracy achieved in their implementation.Peer reviewe

Transverse strength of railway tracks: part 1. Planning and experimental setup

Several studies have been carried out until now by various Research Agencies and Railway Administrations to quantify the effects of the track-bed geometrical characteristics on the transverse strength of the track. Unfortunately, not all the possible scenarios in terms of track components, track-bed cross profile, operating conditions etc. have been investigated and not all the relevant variables have been directly measured.Therefore data available from the literature have different degrees of reliability. With the aim of enlarging the knowledge on the track stability and covering much of the possible relevant scenarios, an experimental research program has been developed in the framework of a cooperation between RFI, Italcertifer and DII.In order to perform the investigation under quite general conditions and to reduce the experimentation costs, n. 28 significant scenarios have been identified and reproduced on as many independent track segments. Byapplying on each track segment a transversal load, the strength of the ballast-sleeper interface has beendetermined. The results relative to the first four scenarios are presented in terms of applied load vs. lateral track displacement diagrams and in more synthetic numerical tables

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

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

Train-Induced Load Effects on the Thermal Track Buckling

Thermal track buckling is probably the major problem due to the advent of continuous welded rail track. In fact, when the rails temperature rises over a critical value, the track can buckle, suddenly or progressively, in the lateral plane. Both poor ballast conditions and large lateral alignment defects are the principal causes of such phenomenon. In a previous paper, a parametric finite element model for thermal track buckling simulation was presented and validated by comparison with analytical results of the literature. In this study, the finite element model has been further validated by comparison with analytical and numerical results obtained by three other authors. Moreover, to take into account the effect on the buckling temperatures of the vertical loads due to train passes, the tie-ballast lateral resistance has been modified along the track, taking into account the vertical reaction forces distribution induced by axle loads. A sensitivity analysis has been carried out both for tangent and curved track, considering two values of the alignment defect amplitude, and different values of the parameters that characterize actual railway vehicles. It is found that the conditions to trigger progressive buckling (△Tmax ≈ △Tmin) are attained with small values of the truck center distance, and in a more accentuated manner in the presence of high values of the lateral alignment defect. △Tmax and △Tmin increase with axle spacing, and this increase is more pronounced for low values of the truck center spacing. △Tmax and △Tmin also increase with curve radius, but decrease for increasing values of the misalignment defect amplitude. In explosive buckling conditions (△Tmax ≠ △Tmin), there is a limit value of the truck center distance above which the vertical load has no more effects, and the results of the static thermal buckling are found