ORCID Profile
0000-0002-3321-2523
Current Organisations
Iran University of Science and Technology
,
University of Wollongong
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: World Scientific Pub Co Pte Lt
Date: 25-08-2016
DOI: 10.1142/S0219455415500406
Abstract: In this paper, a new algorithm for solving the vehicle/track dynamic interaction problem is developed, aimed at reducing the computational cost. The algorithm called Advanced Solver Algorithm (ASA) uses the full Newton–Raphson incremental-iterative method in conjunction with the Newmark integration scheme to solve the equilibrium equations of the coupled vehicle/track system in time domain. Considering the track as a beam resting on a viscoelastic foundation and each vehicle as a wagon with ten degrees of freedom, the governing differential equations of motion of the vehicle/track system were derived. The wheel/rail contact was considered as a nonlinear Hertz spring and consequently the vehicle/track nonlinear dynamic interaction problem was solved. A comparison between the results of the ASA and those of the most advanced algorithm available was made to evaluate the efficiency of the ASA. It is confirmed that using the ASA can result in 40–70 % of reduction in computational cost.
Publisher: SAGE Publications
Date: 12-2009
Abstract: The influence of rail cant on the overall geometry conditions of railway tracks is assessed both theoretically and experimentally in this study. Extensive data obtained from a light railway line are used for experimental investigations. Modelling of rail—wheel contact using the ADAMS/Rail program is undertaken for theoretical investigations. The need to incorporate rail cant into the development of the track geometry indices is identified, and a method of performing this is proposed. Using this approach, a new track index is defined, for which the main geometry parameters, including alignment, profile, track twist, track gauge, and rail cant (rail twist), are considered. For the development of the new track index, these parameters are combined, assigning justified coefficients to each geometry parameter according to its contribution to the overall conditions of the track. The research methodology and the results are discussed. A practical use of the new index is presented to indicate its capability and applicability.
Publisher: SAGE Publications
Date: 13-09-2013
Abstract: Although the loads transferred from a rail to a sleeper and from the sleeper to the ballast have been thoroughly investigated in the literature, little attention has been paid to the influence of superelevation deficiency (SED) on the loading pattern of the sleeper. A thorough field investigation into the effects of SED on the mechanical behavior of railway sleepers was carried out in this research. For this purpose, several load cells were installed above and beneath a sleeper in order to record the loads transferred from the rail to the sleeper and from the sleeper to the ballast, for a railway track with various SED levels. The results obtained were analyzed and a mathematical model for the loading pattern on the sleeper was developed. This model is a function of axle load, train speed, sleeper length and SED. Application of the proposed model in the design of sleepers indicates that SED can have a considerable impact on the sleeper design parameters. Consequently, the sleeper design method can be improved by adding correction factors to the conventional formulation of sleeper bending moments.
Publisher: SAGE Publications
Date: 27-05-2015
Abstract: In conventional design methods for railway tracks, the axle load is multiplied by a term called the load lification factor (LAF). This operation is performed to compensate for the error introduced into the design process by the assumption of static loads. This approach simplifies the design methods and provides a sufficient level of accuracy. However, the available mathematical expressions proposed for this factor have two significant limitations: they account for a limited number of influencing parameters and they were developed based solely on the design criteria of the rail. This research aims at improving the current LAF formulation by addressing these two limitations. Mathematical expressions were developed for the correlations between the LAF and influencing parameters due to the track and rolling stock. These expressions cover the design criteria of the track's substructure components (the rail, sleeper and ballast) and include most of the track and rolling stock parameters omitted in the previously developed LAF formulations. The results obtained in this research pave the way towards a more profound understanding of the dynamic response of tracks and provide practical guidance on how to improve the current methods used in railway track analysis and design.
Publisher: Institute of Noise Control Engineering (INCE)
Date: 03-2022
DOI: 10.3397/1/377016
Abstract: One of the main concerns in the railway transportation is environmental pollutions caused by railway noise. The most important source of this noise is the rolling contact between wheel and rail, and therefore, prediction of the rolling noise is a key factor in the management and reduction of the noise. Despite numerous studies carried out on the rolling noise prediction in the available literature, the role of track components on the rolling noise has not been taken into account. That is, the power dissipation within the track superstructures has not been given sufficient consideration. This is addressed in this research by investigating the influences of the track components on the level of railway rolling noise. For this purpose, a new noise prediction approach is developed in this research using finite element method and the statistical energy analysis. This approach has an advantage of considering power dissipation along the track components compared with the previous approaches. The results obtained from the new approach were compared with field measurements carried out in this research. It is shown that the proposed finite element–statistical energy analysis approach is effective in accurate predictions of the ballasted railway track noise.
Publisher: Elsevier BV
Date: 06-2016
Publisher: SAGE Publications
Date: 02-2010
DOI: 10.1260/1369-4332.13.1.139
Abstract: A comprehensive field investigation was made with the aim of achieving a better understanding of the dynamics of railway track pre-stressed concrete sleepers. Modal analysis and free decay method were used to determine the natural frequencies, model shapes and d ing of sleepers. The validity of the results is discussed by comparing the results obtained here with those available in the literature. In order to investigate the characteristics of the dynamics of the loads imposed on the sleepers, load cells were installed between the rail seat and the sleeper and beneath the sleeper, recording the interaction between both sleeper and rail, and sleeper and ballast. The loads transferred from the rail to the sleeper and from the sleeper to the ballast were measured as a function of train speed. The rail seat load and the contact pressure between the ballast and the sleepers versus train axle loads and train speeds were recorded. The effects of the sleeper supporting conditions on the sleeper dynamic behaviour were investigated. The ratios of the rail seat load and the ballast contact pressure to the wheel load were obtained from the analyses of the field test results. These ratios were used to calculate the dynamic impact factors and ballast-sleeper pressure distribution patterns required for the design of sleepers. The methods, the test procedures and the results are presented and discussed in this paper.
Publisher: Elsevier BV
Date: 06-2021
Publisher: Informa UK Limited
Date: 20-02-2019
Publisher: Informa UK Limited
Date: 09-04-2018
Publisher: World Scientific Pub Co Pte Lt
Date: 06-2019
DOI: 10.1142/S0219455419500603
Abstract: Rail irregularities are the main factors influencing the ride comfort of trains moving over tracks. Despite various investigations made in this regard for the ballasted tracks, there is a lack of studies for the ballast-less tracks. This limitation is addressed in this study. To this end, a vehicle/slab-track interaction numerical model was developed, which was validated by comparison of the results obtained herein with those of the field tests carried out in this study. The effects of rail irregularities with various litudes and wavelengths on the ride comfort were studied by a comprehensive parametric analysis. Particularly, the effects of the wavelengths and litudes of rail irregularity on the ride comfort were investigated. Contrary to the current understanding, it was shown that rail irregularities with short wavelength have considerable effects on the ride comfort for the slab-tracks. In addition, the ride comfort decreases significantly when the wavelengths of rail irregularity become less than 0.75[Formula: see text]m in the metro lines. The critical speed of the train (at which the lowest ride comfort is obtained) was derived as a function of rail irregularity. The results obtained indicate that the litude of rail irregularity has negligible influence on the critical speed of the train.
Publisher: American Society of Civil Engineers (ASCE)
Date: 04-2016
Publisher: Canadian Science Publishing
Date: 05-2010
DOI: 10.1139/L10-010
Abstract: The aim of this research is to improve the accuracy of conventional railway design methods by addressing the main track substructure parameters omitted in the current track design approach. Nonlinear and discrete properties of the track support system were studied and their influence on the calculation of railway design parameters was measured by conducting a field investigation and using finite element analysis. It was demonstrated that wheel loads and accumulative track loading are the key factors influencing nonlinear behavior of the track support system. Mathematical expressions were developed for the impact of the nonlinearity of the track support system based on the track analysis results, and correction factors were established for rail bending moments and rail deflections calculated by current methods. It was shown that the incorporation of these factors improves the accuracy and reliability of the conventional track design method.
Publisher: American Society of Civil Engineers (ASCE)
Date: 03-2020
Publisher: Elsevier BV
Date: 09-2018
Publisher: Elsevier BV
Date: 02-2020
Publisher: Elsevier BV
Date: 10-2022
Publisher: Springer Science and Business Media LLC
Date: 12-2007
DOI: 10.1007/BF03177452
Publisher: American Society of Civil Engineers (ASCE)
Date: 11-2007
Publisher: FapUNIFESP (SciELO)
Date: 2021
Publisher: Thomas Telford Ltd.
Date: 10-2018
Abstract: Significant parts of railway lines in most of the Middle East and Asian countries are in sandy and desert areas. Contamination of tracks (in particular the ballast layer) caused by frequent sand storms in the desert is an important challenge for railway industries. Despite a large number of reported railway accidents caused by the loss of shear strength in the contaminated ballast layer, there is a lack of sufficient studies on the effect of sand contamination on ballast shear strength. In response to this need, extensive laboratory tests on clean and sand-contaminated ballasts were conducted, using a large-scale direct shear test machine designed and constructed in this research. Ballast s les with different dosages of sand contamination were tested. The results obtained are discussed leading to a better understanding of ballast behaviour when contaminated with various amounts of sand. The results show that sand contamination reduces the shear strength and angle of effective shearing resistance of the ballast. The critical percentage of ballast contamination, after which the ballast faces substantial reduction in its mechanical properties, was derived. The results obtained have improved the current ballast maintenance approach by providing the possibility of a more accurate planning of ballast cleaning and renewals.
Publisher: Zhejiang University Press
Date: 11-2006
Publisher: FapUNIFESP (SciELO)
Date: 03-12-2018
Publisher: SAGE Publications
Date: 25-04-2022
DOI: 10.1177/09544097221089417
Abstract: As a practical countermeasure against generally destructive subway-induced vibrations, the injection of a continuous thin layer of soft materials into the soil under adjacent receivers is investigated in this paper for the first time. To this aim, simulations were carried out using a finite/infinite element model of a railway track, tunnel, and surrounding soil. A straightforward analytical approach was implemented to model the dynamic excitation of the moving train. In addition, the effect of a soft V-shaped grouted layer on vibration mitigation on the ground was evaluated via a parametric analysis that determined the impacts of soil type, grout specifications, and train speed. The obtained results clearly indicated that a softer isolator (i.e., the grouted layer) in combination with a stiffer soil provides the best configuration for attenuating the subway-induced vibrations. Furthermore, the injection angle and train speed were shown to have minimal impacts on the isolator performance. Other contributions of the present paper include developing a simple equation to estimate the grouted layer effectiveness and describing how the isolator works in layered soils.
Publisher: Thomas Telford Ltd.
Date: 10-2018
Abstract: Railway track behaviour with unsupported prestressed sleepers has been investigated in the literature. However, some of the important factors – such as prestressing forces, variations of the sleeper cross-section along its length, losing or recovering contact between the sleeper and the ballast layer – have been omitted. These limitations have been addressed in this research. The effects of unsupported sleepers on the dynamic behaviour of railway track have been investigated, using an improved three-dimensional numerical model of track developed here. The validity of the model is evaluated by comparing the results obtained from the model with experimental results (obtained in this research and available in the literature). The influences of the size of the gap between the sleeper and the underlying ballast, the vehicle speed and the number of unsupported sleepers on the track dynamic behaviour were investigated. The effects of the various unsupported conditions of sleepers on the rail seat load, sleeper bending moment and sleeper–ballast contact force at various train speeds were illustrated. It was shown that consideration of sleeper prestress forces, detailed geometry of the sleepers and a more realistic assumption for the sleeper–ballast contact has considerably improved the accuracy of the results obtained from theoretical models.
Publisher: Elsevier BV
Date: 07-2016
Publisher: SAGE Publications
Date: 05-12-2022
DOI: 10.1177/09544097221143824
Abstract: Transition curves are considered as inevitable parts of railways. As they tend to bend the train’s course of movement, the passengers ride comfort and safety are strongly challenged. Although many investigations have performed on the dynamic behavior characteristics of transition curves, only a few studies have focused on the optimum transition length based on the ride comfort index. In response to this need, a vehicle-track dynamic model was developed. The results obtained from model were compared with those available in the literature to prove the validity of the model. Through a parametric study, the dynamic responses of a vehicle passing through the transition curves was studied using the model developed in this study. The ride comfort index was obtained using the dynamic response of the vehicle. The lateral jerk, vertical acceleration, and rolling velocity were considered as the dynamic response of the vehicle. The optimum transition curve length for various configurations of curve radius and super-elevation magnitudes were investigated based on the obtained ride comfort.
Publisher: Elsevier BV
Date: 02-2019
Publisher: Informa UK Limited
Date: 21-09-2017
Publisher: Thomas Telford Ltd.
Date: 08-2016
Abstract: Railway turnouts are important parts of a railway track system which substantially influence train average speed and running safety. Although several investigations have been conducted on improving the geometry of turnout components from the perspective of turnout geometry deterioration, less attention has been paid to the effects of turnout geometry parameters on the safety of train running and permissible speeds. In this paper, the effects of turnout geometry parameters on railway running safety were investigated. The aim was to establish a relationship between turnout geometry parameters and permissible running speeds. For this purpose, a mathematical model of a railway vehicle and a turnout track was developed. The model accuracy was verified through field tests. Conducting sensitivity analyses of the model, the effects of turnout geometry parameters such as curve radius, switch initial angle and track gauge on running safety for various train speeds were investigated. The investigations were performed on turnouts with small and large curves. Mathematical relationships between the turnout geometry parameters and the permissible running speed were developed using the results obtained in this investigation.
Publisher: American Society of Civil Engineers (ASCE)
Date: 12-2010
Publisher: Informa UK Limited
Date: 11-08-2012
Publisher: Informa UK Limited
Date: 08-07-2010
Publisher: Thomas Telford Ltd.
Date: 02-2014
Abstract: This paper investigates the response of railway track to train loads while rested on an embankment. For this purpose, track structure was ided into two parts, in one of which the rail was modelled as a continuous Euler–Bernoulli beam and in another sleeper, ballast and embankment were considered as an integrated lumped masses system. To obtain the mass and stiffness of embankment, the ‘ballast pyramid model' was developed and, consequently, the response of the whole track system was investigated. The vehicle was assumed to be a ten-degree-of-freedom lumped masses system. The dynamic equilibrium equations of the vehicle-track coupling system were solved in the time domain and the track response was evaluated against applied dynamic loads. As a part of the study, a sensitivity analysis was undertaken on embankment parameters, namely embankment height, stiffness and d ing. The results of numerical modelling and sensitivity analysis reveal that, among the aforementioned parameters, embankment height had a remarkable effect on the track dynamic response.
Publisher: World Scientific Pub Co Pte Lt
Date: 02-2013
DOI: 10.1142/S0219455413500089
Abstract: Attention is drawn to the fact that the recent increase in axle loads, speed and traffic volume in railway tracks, as well as concerns over passengers' riding comfort and safety have resulted in fresh challenges that are needed to be addressed. These challenges can only be successfully tackled with a more accurate modeling of the dynamic behavior of railway tracks. Although a significant amount of research involving mathematical modeling of railway track dynamics has been conducted in the last two decades, the nonlinearity of track support systems has not been given sufficient attention. This paper is concerned with the effect of nonlinearity of the support sub-layers on the dynamic responses of the railway track. To this end, a railway track model that considers the nonlinear properties of the track sub-layers is developed. Then, a field investigation into the dynamic responses of the railway track system under moving trains is conducted. The effect of the nonlinearity properties of the track support system on the track responses is investigated by comparing the results obtained by the numerical model, with or without consideration of track support nonlinearity, with those from the field tests. It is illustrated that consideration of the nonlinear properties of the track support system improves the accuracy of the calculated responses by a factor of three. It is also shown that the train axle loads and track accumulative loading have a significant effect on the nonlinearity of the track support system and, as a result, on the modeling of track responses.
Publisher: Elsevier BV
Date: 12-2020
Publisher: Elsevier BV
Date: 05-2019
Publisher: Elsevier BV
Date: 12-2022
Publisher: American Society of Civil Engineers (ASCE)
Date: 08-2020
Publisher: Elsevier BV
Date: 10-2017
Publisher: Springer Science and Business Media LLC
Date: 2012
Publisher: SAGE Publications
Date: 15-04-2009
Abstract: Track geometry, consisting of several parameters, is the main factor influencing the ride quality and track performance. Railway authorities are spending considerably to maintain track geometry conditions within acceptable tolerance. Optimization of this expenditure requires a thorough investigation into the track structural factors influencing the conditions of track geometry. The current methods of track inspection are based on automated inspection of track geometry conditions, using track-recording cars. These methods have their limitations in identifying track structural defects, and in turn, lack the recognition of the causes of track geometry problems. There is a need to develop a track structural inspection and to investigate the relationship between track structural defects and track geometry problems. This research is an attempt to response to this need. The most dominant observable track structural distresses were studied, a track structural inspection method was proposed, and track structural conditions were quantified. A technique was developed to correlate track structural defects to track geometry problems. This technique was applied to tracks with various conditions, carrying out a comprehensive field investigation. The results obtained were analysed to identify the role of each track component on track geometry deviations, and in turn, develop correlations between track structural quality and track geometry conditions.
Publisher: Elsevier BV
Date: 04-2020
Publisher: Informa UK Limited
Date: 2012
Publisher: Informa UK Limited
Date: 12-2011
Publisher: American Society of Civil Engineers (ASCE)
Date: 2021
Publisher: Informa UK Limited
Date: 26-10-2015
Publisher: American Society of Civil Engineers (ASCE)
Date: 11-2016
Publisher: Canadian Science Publishing
Date: 09-2008
DOI: 10.1139/L08-026
Abstract: This research investigates the accuracy of the assumptions made in the current method of analysis and design of railway track sleepers. This study consists of a comprehensive field investigation into the response of sleepers in a railway track system to static and dynamic loads. In the experiments, several load cells (load gauges) are installed under a rail seat and beneath a B70 concrete sleeper for the purpose of monitoring the response of the sleeper to vertical loads. The dynamic coefficients factor, the ratio of the rail seat load to the wheel load and the pressures between the sleeper and the ballast are measured. The results are used to evaluate the current approaches for the analysis and design of concrete sleepers, in particular those proposed by the Americans (AREMA) and Europeans (UIC). New models are proposed for the calculation of dynamic load factors, correlations between wheel loads and rail seat loads, and load distribution patterns beneath sleepers.
Publisher: FapUNIFESP (SciELO)
Date: 2020
Publisher: American Society of Civil Engineers (ASCE)
Date: 08-2010
Publisher: Elsevier BV
Date: 08-2022
Publisher: Elsevier BV
Date: 05-2017
Publisher: Informa UK Limited
Date: 02-2012
Publisher: American Society of Civil Engineers (ASCE)
Date: 08-2017
Publisher: IEEE
Date: 2010
Publisher: Elsevier BV
Date: 04-2018
Location: Iran (Islamic Republic of)
No related grants have been discovered for Javad Sadeghi.