Influence of unsupported and partially supported sleepers on dynamic responses of train–track interaction

Jabbar Ali Zakeri,Morvarid Fattahi,Mohammad Mehdi Ghanimoghadam 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.6

One of the major problems of railroad deterioration is uneven settlement which occurs due to various reasons, including existence ofdefects in substructures, using non-homogenous ballast, or being poorly drained. Sometimes, because of these problems, sleepers remainfreely as a part of vertical displacement and contact the ballast with load increase. Different models have been presented for checking theeffect of hanging sleepers on the dynamic interaction of rail and train. In this paper, a mathematical model was developed for railwaytrack and differential rail displacement with supported and unsupported sleepers was compared by modeling sleepers such as partiallysupported ones. On this basis, the motion equations of the train-track system were solved considering the non-linearity of wheel/rail contactform and using numerical integration in the time domain. Longitudinal sections of the track model were coded in Matlab softwareand the effect of one, two, or three partially supported sleepers and various spacing of sleepers on the sleepers and rail displacement wasstudied and compared with that of the unsupported one. It was shown that, with increasing the sleeper spacing from 50 to 75 cm, raildisplacement increased from 7 to 22% in the unsupported sleeper and 5 to 8% in the partially supported sleeper. Additionally, rail displacementincreased from 13 to 74% by changing the number of the unsupported sleeper from 1 to 9. Also, it increased from 6 to 24% inthe partially supported sleepers.

Investigation on dynamic behavior of railway track in transition zone

Jabbar-Ali Zakeri,Vida Ghorbani 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.2

Railway track transition zone is a zone where track stiffness changes abruptly. This change occurs where the slab track connects to a conventional ballasted track, at the abutments of open-deck bridges, at the beginnings and ends of tunnels, at road and railway level crossings, and at locations where rigid culverts are placed close to the bottom of sleepers. In this paper, ballasted and slab tracks are simulated by two-dimensional model with two-layer masses. The transition zone is divided into three segments, each having a length of 6meters with different specification and stiffness. The model of track consists of a Timoshenko beam as a rail and slab, lumped mass as sleepers, and spring and damper as ballast, sub-grade, and rail pad. The results of the dynamic analysis are presented and compared in two circumstances – one considering the transition zone and the other its absence.

Field investigation of variation of loading pattern of concrete sleeper due to ballast sandy contamination in sandy desert areas

Jabbar Ali Zakeri,Rauf Abbasi 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.12

Sleeper is one of the most important components in a railway track system. Thus, for accurate analysis and design of concrete sleepers,knowledge of imposed loading pattern is necessary. Sandy desert areas are critical regions where loading status of concrete sleeper is different from other areas. In these areas, the influence of flowing sand grains between the ballast aggregates increase the stiffness of ballast layer; consequently, rail support modulus increases, so the received share of total axle load subsequently increases on the sleeper which is placed under the wheel load. On the other hand, the pressure distribution underneath the sleeper changes considerably. In this paper, the results of a field investigation about the variation of rail support modulus and also variation of loading pattern of concrete sleeper followed by the variation of bending moment of sleepers in sandy desert regions were presented.

Sensitive Analysis of Track Parameters on Train- Track Dynamic Interaction

Jabbar Ali Zakeri,He Xia 대한기계학회 2008 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.22 No.7

Dynamic behavior of railway tracks when trains are running is influenced by several factors, i.e. rolling stock, the components of superstructure and their specifications. Usually, features like the sleeper spacing, rail pad stiffness, bal-last damping and stiffness have an effect on the dynamic response of the track. The best method to study the dynamic behavior of the track is to model the track assembly and the train as a whole and carry out an analysis of dynamic inter-action. Such analysis makes the identification of the tracks dynamic behavior easer and helps to anticipate the deterio-presents tracktrain dynamic interaction without considering irregularity of the rail face. A sensitivity analysis was carried out on the selected model. The analysis was undertaken with the view of varying one of the mentioned parame-ters and the results were presented to further identify the deterioration of the track elements. The results indicate that reducing sleeper spacing, rail pad stiffness, ballast stiffness, and increasing ballast damping reduces wheel-rail, rail-sleeper, and sleeper - ballast contact forces. Keywords

Application of 2D-infinite beam elements in dynamic analysis of train-track interaction

Jabbar Ali Zakeri,He Xia 대한기계학회 2009 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.23 No.5

Railway structure is a structure with an infinite length for which its modeling is usually carried out by accepting some assumptions for boundary conditions. In practice, there are various methods of modeling by forming equations of motions and dynamic analysis. One of these methods is modeling the railway track by finite element method. Generally in such modeling, a limited length of a track is modeled and executed by implementing some boundary conditions. Assortment of boundary conditions has an effect on dynamic responses. To reduce such effects, usually the length of the track is chosen to such a measure to minimize the dynamic responses of the end points of the track elements to zero. Doing so would cause an increase in the length of the track and hence add to an equation's degrees of freedom, volume of output and prolongation of analysis time. For this reason, a combination of finite elements and infinite beam elements (two end elements) has been proposed for railway track modeling. Also, matrices of mass, damping and stiffness of one infinite element which has been laid on a visco-elastic bed, have been calculated by implementing selected shape functions. Therefore, by applying two infinite beam elements on either side of the model, a railway track is formed like a beam on an elastic bed which creates the possibility of eliminating the boundary condition effects.

Field investigation on load distribution and deflections of railway track sleepers

Jabbar Ali Zakeri,Javad Sadeghi 대한기계학회 2007 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.21 No.12

Despite the significant role of sleepers in railway track mechanical behavior, no thorough mechanistic approach has been presented for the development of the loading pattern they experience. The current theoretical methods in the analysis of the railway track system need further calibration and verification using field-measured data. In this paper, using specific load-cells between sleepers and the rail and beneath the sleepers, the vertical loading conditions of these main track elements are studied. The lateral resistance of the concrete sleepers in the ballasted tracks is investigated by using full scale sleeper pull-out tests. Moreover, track deflections under the sleeper as the main track analysis parameter are measured and the results are discussed. In this paper, with the results obtained from extensive field measurements, some suggestions are made leading to an improvement in the current understanding of the sleeper loading pattern and the track deflections.

Experimental investigation of effects of sand contamination on strain modulus of railway ballast

Kian, Ali R. Tolou,Zakeri, Jabbar A.,Sadeghi, Javad Techno-Press 2018 Geomechanics & engineering Vol.14 No.6

Ballast layer has an important role in vertical stiffness and stability of railway track. In most of the Middle East countries and some of the Asian ones, significant parts of railway lines pass through desert areas where the track (particularly ballast layer) is contaminated with sands. Despite considerable number of derailments reported in the sand contaminated tracks, there is a lack of sufficient studies on the influences of sand contamination on the ballast vertical stiffness as the main indicator of track stability. Addressing this limitation, the effects of sand contamination on the mechanical behavior of ballast were experimentally investigated. For this purpose, laboratory tests (plate load test) on ballast samples with different levels of sand contamination were carried out. The results obtained were analyzed leading to derive mathematical expressions for the strain modulus ($E_V$) as a function of the ballast level of contamination. The $E_V$ was used as an index for evaluation of the load-deformation characteristics and bearing capacity of track substructure. The critical limit of sand contamination, after which the $E_V$ of the ballast reduces drastically, was obtained. It was shown that the obtained research results improve the current track maintenance approach by providing key guides for the optimization of ballast maintenance planning (the timing of ballast cleaning or renewal).

Field test investigation and numerical analysis of ballasted track under moving locomotive

Seyed-Ali Mosayebi,Jabbar Ali Zakeri,Morteza Esmaeili 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.3

This paper is devoted to investigating of dynamic behavior of a ballasted railway track by field tests and numerical analyses. In this regard, at first in a field test program, two different sections in a ballasted track including concrete and wooden sleepers with good quality are selected and their dynamic vertical deflections are measured due to moving locomotive. In continuation, the numerical model of vehicle track interaction is developed and its results are verified using the measured values in the field tests and the previous research studies. Finally, using the verified model, a series of sensitivity analyses are accomplished on effecting parameters including sleeper type and track modulus. Results indicate that the dynamic behavior of the ballasted track under moving locomotive is linear with concrete sleepers while non-linear with wooden sleepers.

Vehicle/track dynamic interaction considering developed railway substructure models

Seyed-Ali Mosayebi,Jabbar-Ali Zakeri,Morteza Esmaeili 국제구조공학회 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.61 No.6

This study is devoted to developing many new substructure models for ballasted railway track by using the pyramid model philosophy. As the effect of railway embankment has been less considered in the previous studies in the field of vehicle/track interaction, so the present study develops the pyramid models in the presence of railway embankment and implements them in vehicle/track interaction dynamic analyses. Considering a moving car body as multi bodies with 10 degrees of freedom and the ballasted track including rail, sleeper, ballast, subgrade and embankment, two categories of numerical analyses are performed by considering the new substructure systems including type A (initiation of stress overlap areas in adjacent sleepers from the ballast layer) or type B (initiation of stress overlap areas in adjacent sleepers from the subgrade layer). A comprehensive sensitivity analyses are performed on effective parameters such as ballast height, sleepers spacing and sleeper width. The results indicate that the stiffness of subgrade, embankment and foundation increased by increasing the ballast height. Also, by increasing the ballast height, rail and ballast vertical displacement decreased.

A comparison between the dynamic and static stiffness of ballasted track: A field study

Mosayeb, Seyed-Ali,Zakeri, Jabbar-Ali,Esmaeili, Morteza Techno-Press 2016 Geomechanics & engineering Vol.11 No.6

Rail support modulus is an important parameter for analysis and design of ballasted railway tracks. One of the challenges in track stiffness assessment is its dynamic nature under the moving trains which differs it from the case of standing trains. So the present study is allocated to establish a relation between the dynamic and static stiffness of ballasted tracks via field measurements. In this regard, two different sites of ballasted tracks with wooden and concrete sleepers were selected and the static and dynamic stiffness were measured based on Talbot - Wasiutynski method. In this matter, the selected tracks were loaded by two heavy and light car bodies for standing and moving conditions and consequently the deflection basins were evaluated in both sites. Knowing the deflection basins respect to light and heavy loading conditions, both of static and dynamic stiffness values were extracted. Finally two definite relations were obtained for ballasted tracks with wooded and concrete sleepers.